The 3 most important things every programmer needs to know

Version Control with Git

I am surprised to see that even today a lot of programmers are not using version control and many of those who use are afraid of it. I believed knowing a version control system gives superpowers to programmers. These days the most popular one is Git.

Unit Testing

The (mental) safety of programmers is way underrated. One of the best ways to feel confident that your changes don't break anything is to write tests. Lot's of tests. Regardless of your programming language.

Continuous Integration (CI)

The sooner you get feedback the sooner you can fix any issues, the cheaper it is going to be. Both in time and in money. So make sure you have a CI system running your tests. The best would be to known how to configure a CI system.

What are the 3 most important things in your opinion?