I have been toying with the idea of a decade long learning journey, but I'm yet to decide what is that I want to learn. I want to see what difference does a dec

I have been toying with the idea of a decade long learning journey, but I'm yet to decide what is that I want to learn. I want to see what difference does a decade long learning of a single skill make. I can already see how big difference it makes from my experience with my work in Software Engineering, but learning an entirely new skill would be a great and rewarding challenge I feel.