Boiling the Crab: Slow Changes (beneath Sensory Threshold) add up

by RTiberiu3 min read12th Jan 20189 comments



Phenomenon: A live crab, when slowly boiled, will not climb out of the pot.

This is an analog of a known feature in human cognition: humans are not good at observing small changes. We are good at noticing sharp changes.

In this post, I outline a few anecdotal examples. Then, the phenomenon is applied to outside view, why being yourself in dating can backfire, and slowly deteriorating relationships.


Example of Boiling the Crab: Disappearing the Statue of Liberty: A magic trick.

There's a famous David Copperfield magic trick that involves disappearing the statue of liberty before a live audience. The magician closes the curtain, behind which the statue of liberty sits. When the curtain is lifted, the audience is amazed to find the staute of liberty no longer there! The mechanic behind this magic trick is simple: the participants are sitting on a rotating platform, which accelerates below the the audience's sensory threshold. (Source: Poor Charlie's Almanack, by Charlie Munger).

Example of Boiling the Crab: The smell of leaking gas, and a failure of olfactory perception.

A friend of mine named Robert was sitting doing his homework next to the kitchen in the University dormitory. As he was working, someone turned on the gas stove without turning on the flame.

About half an hour later, friend Alex ran into the kitchen, and said: "Holy shit! That gas smell is so strong that I could smell it from the opposite end of the dormitory."

Robert replied: "What gas smell?"


Application: Outside View can observe sharp differences.

An organization, community, or company that lacks outside view may make a series of small changes to their culture, intentional or otherwise. An outsider who comes in will say:

"What the hell?"

Then they point out 10 things that are unusual. Those things may not be bad -- they juts fall outside of normal boundaries.

In this model, the insider is subject to a sequence of small changes from Beginning to End (the boiling crab). The outsider notices the sharp difference, and reacts.

Application: Dating, and being accepted for who you are, is non-automatic. Epistemic Status: Highly conjectural.

"I want to find a girl/boy/other who accepts me for who I am." - a common sentiment.
"Whenever I apply more filters on myself, girls/boys/others that I am interested in gravitate towards me. When I apply fewer filters, my relationships do not last."
"Girls / boys / others don't seem to like it when I'm just being myself."

Many people have traits that are fairly unique, and not found among many other people. Examples might be: shyness in meetups or gt, being transgendered post-op, or posessing speaking quirks from a tight-knit group of friends.

Someone outside one's social circle and/or set of cultural influences will find differences with themselves apparent. In most new social settings, the background for such differences is not transparent. This can cause a feeling of social-mismatch, even if you were (theoretically) extremely compatible as friends or lovers.

Actionable: Boil the crab ;).

Application: A Deteriorating Relationship, and why one of my friend didn't get out of one in time.

A male friend of mine got in a promising new relationship. At first, things were light, passionate, happy, relaxed, and fun.

Two years later, their relationship ended. Mistrust had been building for some time, mostly around my friend's relationships with his other exes. While it was happening, he did not notice. When he looked back, it was obvious things had been falling apart for quite some time.

I was present when he told his story to a less relationship-experienced friend, and she said:

"I would have left that relationship ages ago if I were you. What were you doing?"

Their mutual conclusion: The two friends concluded, as to why he stayed in: The slow boiled crab doesn't noticed. She thought she would not get into that situation: the fast-boiled crab jumps out of the water. My friends' conclusion about the relationship (and the second friend's reaction to it) inspired this post.

There is no claim that all unhappy relationships can be categorized this way :)


I think a lot more falls under this umbrella. Can you think of any time that things happened to you so slowly, that you never noticed until you took a step back?

(For me, norms from academia have started seeping into how I think. For example, I recently became much more concerned about academic status, to the point where it was interfering wiht my happiness. However, I didn't notice when this happened.)

Boiling has a negative connotation, but the concept also applies to positive changes.

Future work:

1) "Uncanny valley" is one tell for small differences that are not actively conscious, but trigger one's internal feelings of difference. Example uncanny face: (courtesy

Feels wrong, man.

A powerful feeling. Absent uncanny valley, an entire slew of changes could occur unnoticed. A predictive or evolutionary explanation for uncanny valley would be much appreciated.

2) "The human mind treats a new idea the same way the body treats a strange protein; it rejects it."

P. B. Medawar

This quote headlines Ralph Merkle's essay on Public Key Cryptography and its societal reaction. The essay is here: Merkle is the director of Alcor cryonics and co-inventor of Public Key Cryptography (PKC).

(This page also contains the most brilliant theoretical computer science idea I've ever seen, which is outlined in his first paper on PKC.)

The P.B. Medawar concept feels related to crab boiling. Sharp changes cause immunal responses. Changes that occur below the sensory threshold do not. I believe sharp changes can also cause certain big updates, which may be harder for slow changes to do. It would be great to have a predictive theory for how communities or people take in slow changes. Perhaps even a book, like: Updating Fast and Slow. :)


Afternote: This is a fresh take on an old concept, which I first read about in Poor Charlie's Almanack. The new pieces are the applications, which developed from a university discussion of how people end up in unhappy relationships without realizing. It was synthesized through a combination of different people's personal experiences.

Apologies if this content is already somewhere on this site. I haven't yet had the attentional bandwidth to look through. At the least, it can be viewed as a fresh take on a familiar idea :)

The discerning reader will find problems in each of the anecdotes and applications. More on this concept can be found in Poor Charlie's Almanack, by Charlie Munger -- a very excellent and underrated book. He calls it boiling the frog, but the principle is te same.