One life trick I learned way too late is that you're allowed to have fun, on your trade or on the side. One should enjoy a few light-hearted or relaxed moments every week. For some reason I was convinced that one should seek productivity at every moment, which is the fastest way to burn out.
Another life trick I've learned is that you are also allowed to:
1. Say no and disagree with people
2. Walk away from any relationship (personal or
professional)
3. Do what you like, believe what you like (as long as you are not harming yourself or others).
4. Move
5. Hire experts to work for you (if you can afford it)
6. Spend your money as you please
7. Engage in conversation with strangers
8. Drastically change your life (new career, new field of
study, etc)
9. Talk to strangers.
It took me a long time to realize that being an adult means taking control of my life, make decisions and being okay with their consequences because _I_ made them.
For most people 8 is difficult because it took them ages to build up to a salary that pays as well as they do now, and they simply can't afford to do that again.
Enjoying life here and now is such an important aspect. For me, bouldering is such an activity. It demands maximum focus on tiny details in order to climb a piece of rock, which is completely pointless to do. Pure fun.