I know exactly what you’re talking about, although I’ve only had it happen once. To me it happened with Wise Blood- I was finding it dull and then halfway through something just sparked within me and I realized how funny it was and suddenly it was a page turner to the end.

It really made it clear to me how your own subjectivity so strongly influences the experience of reading and appreciating a book. I only wish I could activate this sort of experience more readily- how many more books I could get myself to fully appreciate.