Completing something just to finish it despite lack of interest - is called …?

Recently I started reading a novel that I was excited to read. After getting approximately 45% into it, I lost the pace. It started becoming slow and lousy.

I thought to leave it unfinished but it was from one of my favorite writer (Paulo), so why not just complete it just to meet the finish line?

Sometimes we complete work just because we have started it, regardless of its interest. Is there a word or phrase for this situation?

The expression :

Finished for the sake of finishing, may express the idea you want to convey.

• For the sake of something: (from www.macmillandictionary.com)
  • for the purpose of doing, getting, or achieving something

In economics, the sunk cost fallacy is used to describe the tendency to keep investing in something because you've already invested in it, because you feel that to stop investing in it would make your previous investments a waste. This is usually used in terms of money (for example, a manager buys a computer system that doesn't work well, but keeps using it because he thinks that if he doesn't use it, the money he paid for it will be wasted), but it can also be referred to in terms of time, as in your example: You've already spent time reading 45% of the book, so you might feel that to stop reading it now would make the time you already spent reading it a waste. Of course, this is a fallacy because the manager has spent his money whether he keeps using the computer system or not, and you have already spent your time whether you finish reading the book or not.