For me, it was learning English. Although I do make a few mistakes here and there, I’m mostly perfect on it.
The amount of resources you have access to dramatically increases when you know a universal language. I say dramatically because it made me realize how much my native language lacks when it comes to certain topics. The most obvious one to me was tech and computers. Everybody knows how to use Windows but there are very few resources about stuff beyond Windows. It’s actually sad. [insert sad face here]
Was taking 2 gap years in education. Where I worked a year, and took firefighters education for 9 month, where I met my now wife, after that traveled for 2 month, before I continued my education with computer science.