97 Things Every X Should Know

Don't be afraid of your code. Who cares if something gets temporarily broken while you move things around? A paralyzing fear of change is what got your project into this state to begin with. Investing the time to refactor will pay for itself several times over the life cycle of your project.

If you instead explore new languages to expand your mind and get fresh ideas on how you can solve things in different ways, you will find that the code you write in your trusty old language gets more beautiful for every new language you've learned

Golden Rule of API Design fits in: It's not enough to write tests for an API you develop; you have to write unit tests for code that uses your API. When you do, you learn first-hand the hurdles that your users will have to overcome when they try to test their code independently.