I suppose for me, it's finding some sort of meaning in life - it's been rather elusive, and makes it hard to care about any of those; though I can do ten pullups.

For me, goals and meaning are less an innate property, but things that are built over time as the result of positive feedback from direction and momentum. I didn't start with them, but as I try things, my identity changes to hold a goal more deeply.

An analogy is a rock at the top of the mountain. It doesn't have much direction but maybe vague sense that it could be nice to go somewhere and do something. If it moves around a little, it starts to be pulled in a direction, ever so slightly. The Further it goes, the characteristics of the rock change, pulling it more, and repeating the process.

Some combination of the above list should at least give an approximation of meaning. Or keep you busy enough you don't notice its absence.

Somehow the nihilism always creeps in - the older I get the less I seem to be able to believe in anything, as the evidence accumulates that no one else does either. I suppose I'm one of those smart people who the OP suggested has pissed it all away, but I never really got what it was I was supposed to be doing.

I never quite understood nihilism as a problem. Why doesn't it mean that someone has a blank check to impose their own subjective meaning on life?

It doesn't feel like a blank check. You still gotta get up and go to work every day to pay the bills and then do whatever chores you can muster up the will and time to take care of.

I was thinking about meaning. My understanding is that nihilism is more about a lack of higher purpose, opposed to a lack of action.

I agree that work and chores are tough if you don't have a reason to be doing them. Similarly, will and motivation also require a goal, so that would be a challenge without one.

> Why doesn't it mean that someone has a blank check to impose their own subjective meaning on life?

I never understood Existentialism as a serious proposal.