In the end it does not matter whether you re-read A. Christie's complete works thrice and did not finish Brothers Karamazov or vice versa.

Personally, I have a hard time not finishing a book, for example I can't decide whether I want to continue reading Gone Girl past half. This book is written cleverly yet somehow disappointing after the first big twist(it came too early imho).

One strategy I employ is reading three or four books at a time, one sci-fi, one mystery, one science, one philosophy one political and so on.