When you're the type of person who commits.
Me, after watching 8 seasons of some idiotic streaming show.

"I just wanted to know how it ends!"

It never really pays off, just read a summary.

Supernaturals
Assuming you mean Supernatural, while I didn't care a lot for the Leviathan storyline, I'm glad that I made all the way through since it picked up again after except the very last episode which I didn't care for. Ending on the second to last episode would have been perfect for me.
season 5 was suppose to be the true ending, because of kripke, he gave up after people wanted to continue it. outside of 8, and 11, every other season was pretty bad. also jack was apparently shoe-horned instead of using jessie turner as the anti-christ in the show.