>I'm increasingly seeing people around me give serious thought to this question. Figuring out what to do in life? I thought I had figured things out, but now when I think again I feel doubtful. So, how do you "figure" things out in a way that it's bulletproof.

This is something they fail to teach in school because teachers tautologically don't know the answer.

Entrepreneurs also don't quite understand and often fall into serial startups until 1 works. Eventually they learn.

Marcus Aurelius has something to say: https://www.youtube.com/watch?v=L-STKInWhpU

Here's probably the going book: https://lettinggobook.org/

Arnold's video: https://www.youtube.com/watch?v=u_ktRTWMX3M