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]
Marrying my wife. She is so smart and strong. We make a great team and we have been able to resolve the various conflicts of 15 years. I couldn’t have chosen a better partner.