One of the most valuable concepts I learned in school: Opportunity cost -...
One of the most valuable concepts I learned in school: Opportunity cost - The loss of potential gain from other options when an option is chosen.
This is why getting comfortable with saying "no" is important.
Every "yes" is an implicit "no" to something else.
Example: Every skill I choose to learn means I have less time to go deeper on the skills I already know.
I specialize in front-end dev. That means I have to say "no" to many opportunities.
The opportunity cost of going too wide: I wouldn't have time to go deep in my speciality.