Rule of reading

When I read a book, I have a simple rule. I read a minimum of 75 pages before I decide if I will finish the book. I'm "of an age" now where I can't waste my time reading books that I don't like. They might be perfectly good books, (Some have come highly recommended, bestsellers, critical praise.) but I just don't like them. I think 75 pages is a fair shake and still doesn't waste my time on a book that I don't enjoy.
Sometimes the silliest things will turn me off of a book. And frequently, the higher the praise the harder the fall. For example, Wicked: The Life and Times of the Wicked Witch of the West by Gregory Maguire was cast aside for the inability of my mind to grasp the Munchkins political and social strife. Audrey Niffenegger's The Time Traveller's Wife got the boot because I couldn't get past the naked 30-year-old man approaching the 6-year-old girl in the meadow.
I know these are both good books. I will fully admit they are well-written and thoughtful. Most of the readers of these books came away greatly enriched by them and thoroughly enjoyed them. The reasons I gave up on these two are trivial, but for some reason, loomed large in my head as I tried to struggle past them and give myself up to the stories. Because that's really what we're doing when we read, right? We submerge ourselves into these stories the way you sink into a big warm bath. I do it to the point of becoming annoyed if a character does something that's not in keeping with his or her nature.
Something out of character gets under my skin and turns a lovely dive into a good book into a tepid dip in a cold tub. Hence the rule. 75 pages.