To get your mind around purpose, I have three things I think of as the "willpower keys." These purpose keys are constructed in the same way the human brain is constructed; of three parts:

Your Biological Imperatives: these are the basal, primitive needs you must fulfill as a biological organism. Fulfilling them brings pleasure, and ignoring them brings pain, or even death, of the most immediately impactive variety.

Your Emotional Needs: these are the needs you need to fulfill emotionally. Failing to fulfill them leads to depression, while fulfilling them leads to life satisfaction.

Your Logical Wants: the only needs you "control" - these are needs like "learn a sport" or "build a business" or "climb that mountain." Logical wants are built on top of and stem out of biological imperatives and emotional needs. They can sometimes become emotional needs if they are worked on hard enough over a long enough period of time with enough emotion invested into them.

Just like how the brain works, these three keys generally yield to the keys beneath them that are holding them up:

Your emotional needs will yield to your biological imperatives

Your logical wants will yield to your emotional needs and biological imperatives

That means, if you logically decide "no more chocolate," but your body decides it needs what chocolate has, you're probably going to eat that chocolate.

BIOLOGICAL IMPERATIVES

Your biological imperatives are as follows:

Don't die

Eat food

Drink water

Maintain homeostasis

Mate and reproduce

Avoid pain

Seek pleasure

Religions are successful because they primarily appeal to our biological imperatives, which are our strongest internal motivators:

All religions promise an afterlife - in effect, that you never really die

Boundless food and drink are often promised in this afterlife - a paradise

In many religions, sex is promised in the afterlife (e.g., Islam’s 72 virgins)

In most religions, adherents are told to have many children and be "fruitful"

In the paradise afterlife, there will be no pain, and all will be pleasure, forever

The easiest way to both wear yourself out in the short term and toughen yourself up over the long term is by avoiding fulfilling your biological imperatives. A man who goes without food for three days becomes very weak, and his will disappears almost entirely; however, once he has done this repeatedly and learned to fast like this, his willpower reserve grows larger than most men's ever will.

Generally speaking, you can only ignore biological imperatives for short periods of time. The longer a biological imperative is ignored, the more likely you are to have your reptilian brain take command of your mind and body and fulfill its will despite what your neocortex thinks it wants.

This is why you so often see:

Dieters fail on their diets (eat food)

People give up working out (avoid pain)

People become addicted to drugs (seek pleasure)

People who think they don't want children grow weak for a partner and get married and have children (mate and reproduce)

Fighting nature is good to do in short bursts to build your willpower up.

But trying to fight a war of attrition against nature over a sustained period of time will run your willpower out and force nature to take control of your body, on the assumption that your neocortex is taking you too far astray from doing what you are supposed to do, and it's time to get you back on track.

EMOTIONAL NEEDS

Once your biological imperatives are fulfilled, you're free to set to work on your emotional needs. Your emotional needs are the objectives stemming from your mammalian brain. These include:

Be included

Be liked

Be loved

Be needed

Be respected

Be revered

Be understood

Learn new things

Experience new things

Explore new stimuli

These needs become comparatively unimportant when your biological imperatives are not being met. They quickly fade away into the background.

If you have many friends from poorer countries, or have traveled to poorer countries outside the developed Western world, you'll quickly notice that nobody, really, is depressed, and mental illness is far less a scourge there than it is in the West. Why is that? Because everybody's working so hard to fulfill their biological imperatives that they don't have much time to worry too much about whether they're respected or understood.

You don't start seeing too much of those concerns in poorer countries until you come into contact with - you guessed it - the wealthier citizens of those countries, with fewer immediate concerns to deal with and more free time to spend introspecting and wondering why they don't have this emotional need or that emotional need being fulfilled.

Unfulfilled emotional needs are the font from which victim mentality rears its head. People scrambling to survive don't have time to worry about whether they're victims or not. But people whose survival is assured, but emotional needs unmet, often become mired in seeing themselves as victims of the uncaring masses, left behind to rot.

LOGICAL WANTS

Your logical wants are what you end up with when you calmly and rationally look at your biological imperatives, and look at your emotional needs, and look at everything that's going on in the world right now, and decide what it is you should take on, do, or achieve.

Logical wants are usually "best guess" efforts at satisfying your more basal needs. That is to say, most people are not aware - or are in denial about - their more primitive needs and urges (i.e., the people who say, "I'm not afraid of death!" or, "I don't care if the whole world hates me!" or, "I love being the outsider!")... which means that most people choose their logical wants in ways that do not align with what they actually need and are compelled to do.

For a long time, religion solved this problem the vast majority of people - religion simply took your logical wants over, and told you what to want, and what it told you to want was in line with your biological imperatives and emotional needs.

However, we've thrown off the yoke of religion and are now trying to redefine what it is we want for ourselves. What's the purpose of life now that we no longer have religion to adhere to?

In trying to determine their own wants, people are ignoring the wisdom of thousands of previous generations of their elders and trying to do it all alone, all by themselves.

Not exactly a recipe for total fulfillment.

IGNORE YOUR KEYS AT YOUR OWN PERIL

The most successful people you will ever meet in life are not those who say, "I do NOT want this!" and, "I do NOT want that!"

They are also not those who say, "I can do anything I want to do!"

Rather, they are the ones who say, "I am human, I am very limited in my willpower, I have a great many urges I cannot control and may not even want to control, and I simply have to work around my nature as a man to achieve the things I'd like to achieve."

Fighting against yourself is a battle you will lose. You can sometimes redirect energy or urges, but you can never block them for long.

Nature is very good at taking control of those people who are trying to fight their natures instead of looking for ways to proactively satisfy their natures.

Know what your body and your emotions need, not just right now, but what they will need five years from now, 10 years from now, 30 years from now. What will you want when you are old, dying, and alone? Work proactively to meet those needs now, and keep them met, and you will not have to worry about your mammalian or reptilian brains seizing control of you to make you do things your neocortex thinks it doesn't want you to do for whatever logical reason it's settled on.