I use Mortimer's system for non-fiction works, which is where it makes the most sense.

I would also use it if I was doing a really deep dive in a fiction work.

For most fiction that I am reading for entertainment, the first 50ish pages will tell me if its worth finishing.

Decent way to do it. I usually try to read the first 2-10 pages of a fiction book (at most) before I decide I might like it. If it hooks me, I open to two other mostly random pages, and ignore the plot parts to see if the writing style still seems good. If so, I buy or borrow it (depending).

Non-fiction is different (aside from reasons already mentioned) in that there is usually a far more limited number of books on a subject anyway. Sometimes (mostly not textbooks), you are stuck with just one or a few. Lots of great little obscure books about quirky bits of history out there that were great twenty pages in, but started out sorta meh.

Read the Adler book in high school; I kinda felt it was overrated at the time. I probably ought to reread it as an adult (not a 15 year old) at some point.

> For a lot of fiction books, my rule is to read the first 50 pages. If I'm not engaged, move on. Life is short.

Just encountered myself doing this. I was reading John Birmingham's Axis of Time books. The first three sucked me in and I devoured them in a day or two apiece. Starting the fourth...something was off. The writing felt stilted, like the author was trying to cram in too many pop culture references or something. I put it down and have given it two more tries since with the same result, so now I'm done.

I'm sad, because I was really looking forwards to having several more books in the series.

Yes. It fundamentally changed how I read a book. I go back to it every once a while and always find new things to apply every time.