Another day, another new gamedev skill unlocked

Another day without a job, another skill unlocked :)

Today I managed to make a working shader for the dotted outline around our main character's text box.
It's a small thing, but it's incredibly satisfying to see ideas that existed only in your head slowly start working together and becoming an actual game.
Programming definitely wasn't the most obvious skill for me to learn as an artist, but I've been surprised by how much I enjoy it.
Game development keeps pushing me to learn things I never expected to touch.

What skill did you start learning only because your game needed it — and ended up actually enjoying?