I read a lot of books, but I start probably twice as many as I end up finishing. In the last three days I've started and stopped three books.
I just can't see slogging forward, wasting my precious reading time, if I'm not really into the book, if it doesn't have a grip on me. It wasn't always this way. For one thing, I so do not subscribe to the editors' and agents' mantra that it's all about the first page. Many books take a while to build up steam, and a serious reader has to let the process unfold. I can be patient, and in the hands of the right author such patience will be rewarded. So I used to rarely close a book without finishing; when I did it usually wasn't until after I'd read a good 150 pages or so, until, in other words, I'd given it every chance to win me over. I was always full of hope. I always thought the book might catch fire on the next page.
But some while ago I read a great formula for when to give up on a book you're reading, and it has freed me. I no longer feel required to keep reading if I'm not loving it and I no longer feel guilty about the decision. There are too many great books waiting to be read and I'm getting too old to waste my time on the not-great ones.
So here's the rule. It's all about how old you are, which seems right to me since you young'uns have more reading years ahead of you.
If you are under 50 years old, you should read the first 100 pages plus your age. For example, if you're 38 you should read 138 pages before giving up. Invest the time. You've got plenty available. It may appear odd that with this approach, younger folks get off with reading fewer pages and you have to read further in the older you get until you hit 50. Think it over, though, and it makes some sense. It has to do, I believe, with growing into your powers as a reader. With maturity.
The rule flips once you are over 50. Read 100 pages minus your age. Time's a-flying. Move on. You're wise enough--now wise up and stop wasting your time. In my case, this means I can give up on a book at page 46. Sweet!