This is something that clicked after a few hours rather than a few years, but it is similar in a way. A long time ago when I was a graduate student I was in the library one afternoon studying some idea in field theory (physics). It covered maybe three pages in a small book, but it wasn't making any sense. Finally, hours later it suddenly became clear, and it was so simple. I remember saying to myself, "Why didn't they just say that?" I looked back at the book and they said exactly what I would have said. I guess sometimes words are not enough.