I have found that mine often come back around, even if it's many years later. Which is nice because I already have a bunch of books or whatever on the subject, though I had previously barely touched them. So this time I might read a few chapters. Or even the whole book! - I've noticed my attention has gotten somewhat better as I age. Many topics I've returned to 2 or 3 times now. It was really helpful for me to realize that. Yes, it's an extremely long list, but it is not infinite or completely without structure.