There are lots of valid reasons not to finish a book. There are big ones, like when a book is offensive to your beliefs, or has opinions and perpetuates stereotypes that you find toxic. There are practical ones, like the book falling behind a bookshelf and you feeling too weak to move all the books so you can move the shelf and rescue it, or it falling behind the radiator of a little used room causing you to wander the house sadly and hopeless not finding it. And then there are the very small reasons, that make you wonder if should keep giving the book a chance, even though you know it will probably not work out well.
For instance, I have just put down a book at the start of the third chapter for the following small reason--
This might be a deal breaker for me. It seems to me that the author wasn't really thinking of her tree as an oak tree after all. And if the author can't keep a tree straight, and if the copy editor didn't catch it, what other inconsistences and wrong details will there be in the rest of the book? I can no longer trust the author to smoothly deliver quality world building, and I am not inclined to keep going.
If the oak tree really seems meant to have been an apple tree, I'm not sure it's worth going on.
Am I being too picky? The book was ok otherwise; not great, but reasonably interesting....