What you'll never see

We get used to the smell of our own house. So much so that we sometimes don't even realize that the smell might be unpleasant.

Writing can be very similar.

Sometimes, you've lived in your story so long that you don't see its faults anymore. You don't see the plot holes or that some of the actions come out of nowhere.

You miss a lot when it's something you're too close to. So, get someone else to help and point out what you yourself could never see.