Care and Feeding
Why don’t they teach you to deal with complicated emotions and hard situations in school?
I know the answer to that, obviously; dealing with it is complicated, and it’s also different for everyone. It’s fluffy and non-fact based and can’t be tested for and assigned a grade.
But seriously, having a reliable guide for Care And Feeding Of Your Human Body And Mind is the most valuable thing I can imagine. It would have a civilization-scale impact. Whoever comes up with it first should get a Nobel prize.