For some reason, this is how things have gone for me lately with the middling to long single player games.
Buy the game and play a ton of it in one sitting. Don't finish it, because it's too long for that.
The next day, I forget to continue playing! How? Maybe that day I watched movie or a hockey game instead. Maybe I didn't enjoy any media at all that next day, and podcasted, cooked dinner, etc.
The next time I sit down to enjoy media, the game does not come to mind. I forget about it completely.
When I do remember the game and regret buying it, I resolve to finish it to get my money's worth. Oh no! It's been to long. I forgot the beginning. I don't want to replay the beginning. I MUST replay the beginning because I forgot everything. And now I'm not going to play at all.
I have a nice pile of single player games I've never finished. This started a long time ago. I think the oldest unfinished game in the queue is Golden Sun 2 for GBA. I beat almost all the GameCube games I had, but not all the Wii/DS/Steam games.
Occasionally a game comes along that is good enough that I beat it. This is how I've beaten every Zelda game. It's too good for me to forget it the next day. Same with DOOM(2016).
This year is going to be the year where:
1) I finally dispose/sell/give away video games/board games/comics that I don't need in my apartment.
2) I already greatly reduced buying in 2016, but I'm going to buy even less in 2017. My monthly comic box only has a handful of comics in it these days. Even if I get a Switch, I'll get only the games I know for sure that I will play a bunch. For example, I probably won't Splatoon. Not because it isn't good, but because I know I won't play it enough.
3) Actually go and play/read/finish things in the queue. Use reminders when I leave off so I remember to continue the next day.