Settling for Average

I finished listening to an audiobook yesterday of a science fiction novel and I was... well, let's just say I was underwhelmed. 

The book itself wasn't bad, really, it just wasn't that great. It held my attention with occasional bursts of good writing and interesting concepts, and the hope for a satisfying conclusion. But it didn't deliver. Turns out it was only part one of a three-book series. I'm not interested enough to stick around for the conclusion. In fact, I'm a little disappointed that I invested the amount of time that I did into something that was so mediocre.

What is it about us (maybe just me, but I'm guessing some of you are the same way) that we stick with something because we are completists, even when the content is only average. We all have a limited amount of time, but we stick it out with books, TV series, etc. because we think, "Well, I started it, I might as well keep going to the finish." 

Is it optimism that it will get better? Or is it a fear of missing out? 

Is there something to be said for persistence? 

Are we just worried about sunk costs?

I don't know. I'd love to hear some comments from you. In the meantime, I'm going to try to be better about cutting bait (so to speak) and jettisoning the average so I can invest my time in the above average or the excellent.