Ask HN: What you wish you'd known

Compiling resources to share with developers who are just starting out or people interested in learning about programming and computer science.

So, the question would be:

What tools/ideas/articles/books/#{anything} do you wish you had known/had/been told etc. when you were first starting out?

Looking to distill all I can, so even a helpful maxim that changed how you think about programming could be really helpful.

Thanks all!