Learn to be difficult when it counts
You can lose money and make it back, you can't do that with time.
If the challenge we face doesn't scare us, then it's probably not that important.
The best way to improve mental performance, is to improve physical performance
There are two components that are fundamental to enjoy life and feel good about yourself: continual learning and service.
The downstream effects are unknown. Do your best and hope for the best. If you're improving the world-however you define that-consider your job well done.