Why do brilliant novels so often fail at the finish?

A disappointing ending to a novel you've been enjoying has a peculiar power over us. At least it does for me. 

You can spend days immersed in a novel, recommend it to friends before you've even finished it, and carry the characters around in your head. Then you reach the final chapter and something doesn't quite land. The ending feels rushed, overly clever, relentlessly bleak, or simply at odds with everything that came before.

It raises an uncomfortable question. Can a bad ending ruin a great novel? I'm asking as I have read a slew of novels recently where this has been the experience.

The comfort of unlikeable characters and why we do not need to like who we read about

There is a particular kind of discomfort that comes from spending time with characters you do not especially like. They make poor decisions. They frustrate. They resist redemption. They say the wrong thing, choose the wrong person, protect themselves when they should reach out, or pursue what they want with a moral flexibility that makes you shift slightly in your seat.

And yet, more often than we might admit, they are the ones who linger. I can think of so many books that are true of this, and we always reach for them.