I bought my first Java book when I was 23. I wasn't trying to "study concurrency," or "learn threads," or check any box. I wanted to make a nonogram — a paint-by-numbers logic puzzle, the kind where number clues along the rows and columns tell you which cells to fill in to reveal a hidden picture.
What I'll add up front is the pace. I'd just quit my previous job, so I had nothing but time, and I spent almost all of it studying — every single day. It came to about six months, though I never set that as a target; it's simply when I started wondering whether I could find work in Java. Progress was embarrassingly slow. I'll say this plainly because it matters: nothing came quickly for me. What I had was time, daily repetition, and something I wanted to build.
Looking back, that's the whole story. Everything I know about concurrency, I learned because something I was building stopped working, and the only way forward happened to be the next concept up. I never read the threading chapter because it was next in the book. I read it because I wanted a stop button.
This is a description of that staircase — the one Java quietly built for me, where each step was pulled into existence by a problem on the step below it. I think the staircase matters more than any single step. So let me walk up it the way I actually climbed it.
