Crossposting the entire thing from Putanumonit in honor of the Slack sequence.

Go read Slack, it’s short and important.

If you’re not a slacker, that post might change your life and explain why you feel like you have no control over your own life despite doing well on almost all counts. If you are a slacker, like me, this post gives our philosophy a name and provides a definition: slack is the absence of binding constraints on behavior.

Zvi’s post is abstract on purpose. I’ll continue his mission by getting more specific and, of course, by putting a num on it. To the latter purpose, I’ll modify the definition of slack to make it quantifiable:

Slack is the distance from binding constraints on your behavior. 

Keep your Distance

Slack is a function of many resources. Running out of any single vital resource is enough to constrain your behavior: make you do something you didn’t want to, or prevent you from doing something you want. Freedom requires having spare time, spare money, spare energy, spare weirdness points, available friends etc.  The “slack as distance” formula looks a little something like this:

Slack disappears when the spare capacity of any single resource goes to zero, regardless of how much of everything else you have. Maintaining slack requires balancing all the important resources, making sure to shore up the scarcest resources first.

My grandma just paid to replace a pipe on her floor that was flooding the entire apartment building. The other 20 tenants were supposed to participate in the cost, but due to diffusion of responsibility and greed, they decided collectively to weasel out of contributing. A lawyer suggested that my grandma should go to court but she refused, for reasons of slack. The question isn’t whether the time in court will be worth the money gained, but whether the lack of this particular sum of money will force my grandma into something as undesirable as spending weeks litigating against her neighbors. It almost certainly wouldn’t.

At her age, my grandma’s scarcest resource is stress-free time. She’s not trading it for money.

It’s remarkable how many people fuck up by doing the opposite: concentrating on the resources that are easiest for them to obtain, and neglecting their most pressing needs.

One half of Americans have less than $400 to spare, including millions of middle-class people who make and spend tens of thousands each year. The author of this shocking article is an educated professional and a family man. He has accumulated many achievements, but he forgot to save any cash to pay the water bill. On the other side, I have friends from business school with six figures to spare in their bank account and not a single hour to relax.

Whatever resource is scarcest for people is probably the one they aren’t good at dealing with, and for this reason, thinking about it is aversive. It’s easier just to ignore it. But an ignored constraint doesn’t go away, it still binds you.

Currency Exchange

When no single resource is very scarce, you can keep it that way by figuring out the exchange rates between resources and making trade-offs based on those. Trading-off “life currencies” is a subject I discussed in detail before, but slack-based thinking offers a good way to calculate the correct exchange rates. For example: how much is an hour of free time worth to you in dollars?

The slack-based exchange rate is [spare money] / [spare time], when the definition of “spare” is derived from the definition of slack. Spare X = how much X you can lose before being forced into undesirable behavior.

Example: you make $60,000 a year, put $15,000 in retirement, save $5,000 in cash and spend the remaining $40,000. Of those, $30,000 are for necessities and $10,000 are for things you can live without like fancy clothes and expensive restaurants. This means that you can cover your necessities for $45,000 and since you make $60,000, that means you have $15,000 a year in spare cash. That’s how much money you can give up before being forced to change your lifestyle significantly (e.g. move to a cheaper apartment) or jeopardizing your retirement.

Do the same math for time spent: let’s say you spend 10 hours a week on activities other than those you have to do (work, sleep) or those you really want to do (ping pong). These 10 hours a week (or ~500 a year) aren’t the entirety of your free time, they’re the hours you can afford to lose without having to sacrifice important activities.

In our example, $15,000 spare money each year and 500 spare hours imply an exchange rate of $30/hour. This is a good baseline to consider trade-offs against.If you can pay a maid service $75 to save you three hours of house cleaning ($25/hour), you should take the opportunity because you’re converting money to time at a good exchange rate.

Notice that once you’ve made a trade-off, the exchange rate shifts. If the cleaner comes once a month it saves you 36 hours each year and costs you $900. You now have $14,100 to spare and 536 hours, so the new implied exchange rate is 14100/536 = $26.3/hour. Money became scarcer relative to free time, and you’ll be less inclined to keep trading it away.

One danger that lurks when calculating the trade-offs is forgetting about the important resources that are hard to measure. A while after my friend hired a housekeeper, his girlfriend remarked that if they had done this earlier she probably would have had a lot more sex with him. What’s the resource that was binding the girlfriend before the housekeeper showed up? I don’t think it’s spare time or even energy. If you spend your last hour and ounce of energy dusting shelves instead of making love, slack isn’t the problem in your relationship.

So what is it? As usual, we shall find the answer in the ancient teaching of the Hebrew sages.

Abraham and Three Angels, Fiasella Domenico

The only time in the Old Testament when God tells a bald-faced lie is when informing Abraham (age 99) and Sarah (88) of their upcoming pregnancy. When Sarah hears the news she laughs incredulously, wondering how can she have a son when “… my husband is old” (Genesis 18, 12:13). But when God informs Abraham of Sarah’s reaction he quotes her as saying “Will I really have a child, now that I am old?”. God obfuscates the fact that it’s Abraham’s age she laughed about.

According to the Talmud, this story teaches the importance of “peace in the family” (shlom-bayit). It’s a resource so important that it’s worth God lying to preserve it. Shlom-bayit is hard to quantify, but your behavior is as constrained when you’ve lost your partner’s goodwill as if you were down to your last dollar or minute. When maintaining your slack according to formula, don’t forget to count the uncountable resources too.


I find it much easier to untangle my earphones when I hold the entire cable in a loose lump in my hand so that none of the wires are pulled taut.


One of the main things that slack gives you is optionality, the freedom to change your plans. The value of optionality varies a lot depending on what one is up to, whether you’re exploring or exploiting. “Exploit” is when a single best option is available to you, and you pursue it single-mindedly. For example, I’m starting an internship at a dream company in a few weeks, and I will care about nothing except getting a full-time position there. I won’t be intersted in other employment options, and I won’t need slack for anything besides work.

“Exploration” is when a lot of paths are open, when there’s great potential but little certainty. That’s when slack is valuable, it allows you to pursue the opportunities. I learned to appreciate slack in my own life after messing up a critical exploration phase due to slacklessness, my college years.

When I was 18, I joined a very selective academic officer training program. We pursued a double degree in math and physics condensed into three years, along with intensive military training and enough chores to be a bummer. We had negative slack: no money, no freedom, and a daily to-do list that would take about 20 hours to complete, but only if you were fresh off 8 hours of sleep. I dropped out after a hectic two years. I realized that not only did I remember almost nothing from the classes, I didn’t even know if I liked physics, or the army, or if I actually wanted to be an officer.

The same year my wife-to-be enrolled in a community college without much pressure to do anything other than study and to try stuff. She made lifelong friends, learned Japanese, tried out a bunch of subjects and eventually discovered and fell in love with biology. Then, she could shift fully into exploit mode: she aced all the available biology class, transferred to a good university where completed a degree in biology in two years, and got into a leading graduate program. She became a biologist because she had several years when she didn’t have to decide what she would become.

I made up for my slackless undergrad experience by going to a slack-friendly business school. I had time to play every single intramural sport, go on a lot of drunk dates, and become a regular writer for a satire magazine which I spent more time on than all my homework combined. Writing satire later turned into a paying gig, a short but exciting stand-up career in NYC, and eventually Putanumonit when I couldn’t get anyone to pay to hear my jokes. This blog only exists because in the last few years I’ve guarded my slack jealously.

And yet, I see smart people in elite universities fall into the same trap I did originally. Very prestigious schools are very competitive, and competition will incinerate every bit of slack you have. Heavy course loads leave students little slack to fool around with satire, squash, or even fooling around. Once you start pursuing a major there’s little slack to learn anything else, and once you graduate with a load of debt there’s no slack to do anything but take the first paying job on offer. A less prestigious university that requires half the time, the effort and the money of an elite school often offers a better education simply by leaving you with slack and the freedom to explore.

The same is true for other exploration activities like travel (on long trips, I try to leave 50% of the days unscheduled), job hunting, and dating. Slacklessness brings desperation, and desperation leads to making the sort of choices that your friends will shake their heads about a decade later. Fight for your slack, and give yourself it.

Amos Tversky Said

The secret to doing good research is always to be a little underemployed. You waste years by not being able to waste hours.

How much time did he waste coming up with this pithy aphorism? It was worth it.


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5 comments, sorted by Click to highlight new comments since: Today at 5:02 AM

Promoted to frontpage.

I have questions about your formula:

Division by zero?

If I have no spare money, then my slack is… undefined? The formula would seem to require division by zero in that case; that seems strange. (I assure you, it is possible to have no spare money at all, so this is not merely an academic edge case.)


The question of units presents several problems:

  1. What are the units of “spare time”, “spare money”, and “spare energy”? This is important, because the choice of units determines where the inflection points of the parenthesized components are—which, in turn, affects how the components trade off against one another.
  2. The inverse of “spare time”, presumably, is “spare speed”. The square of “spare speed” must then be “spare acceleration”. Fair enough. However, it is less clear what the inverse of “spare money” is (or its square), or what the inverse of “spare energy” is (or its square).
  3. Is “spare energy” being measured in joules, or (as seems more likely) are we speaking of metaphorical “spare energy”—willpower, perhaps, or something like it? I am not aware of an accepted way of measuring such a thing; is there such?
  4. How does one add quantities of these disparate units? Is there a conversion rate? (The “exchange rates” described in the post do not seem to suffice to add squared inverse units. Is the idea that we first convert everything into one units, and then apply the formula? But that makes the formula largely redundant, does it not?) What do the units of “slack” (and of “scarcity”) end up being? (You mention “distance from binding constraints”, but that doesn’t quite clarify; is there a defined metric space, here?)


It would seem that the term “scarcity” is being used here in something other than its usual meaning (or, I should say, any of its usual meanings—whether colloquial or well-known technical). However, unless I missed it, the term is not defined (except in the formula, which merely says that it’s equal to 1 divided by “slack”… but that doesn’t make the matter any less murky). What is the meaning of “scarcity” in this context?

In response to the Division by Zero question, I think the right answer is that slack is zero in that case.

Here's why. Take one of the components, say spare money. As spare money tends to zero, scarcity diverges off to infinity. Therefore slack, which is 1/scarcity, tends to zero as well. So this formula is defined for all values of spare money except zero, and at that point the limit is defined. I would recommend simply filling in the gap.

Is there supposed to be a link here?

Ah, yes. Sorry for that. We have a bit of a weird crossposting setup with Jacob's stuff. Added a link.