Endless Space. Have 50+ hours and a huge empire. Tried getting back into it a few months ago and was totally lost. So many menus, spreadsheets, etc, forgotten where everything is and would have to relearn the whole thing all over again. Also have games I haven't played for the same reasons, mostly rts, sim, strategy type games

Ocarina of Time. Go stuck [on Wii, bad arrow aiming] at the beating drum boss after 100s of tries. 18 months later I DL'ed on WiiU [for $2.00] and started over and finished it.

Yep. Several, actually. In the past few years alone, I have put down the following games, only to pick them back up and finish several months later:

-Fallout 4. Got bored after three hours, put it down for about eight months. Once I picked it back up, it clicked and I put several hundred more hours into it!
-GTA V: It felt like a slog, at first, so I put it down. After about a year or so, I picked it back up and stuck with it. I hated seeing it end!
-Dark Souls III. Having devoured Bloodborne, I had a tough time readjusting to the Dark Souls mechanics, so I moved onto a few other games. One of the games I went to was Dark Souls 1 (again). After a few months, I went back to DS3 and beat it twice, back to back.

Sometimes I get stuck on a boss. A ridiculously hard boss. I'm not that much of a fan of super difficult portions of games that require absolute perfection, almost like 3 starring Mario Kart 8 at 200cc level of difficulty just to progress in a game. I'm looking at you Hollow Knight. I love your gameplay, but you're making me become an expert at dodge and parry and I just want to run and slash and get new abilities, yo. So I put it down months ago, and every time I look at the game I'm reminded that A, I have to beat that boss, or B, I have to figure out where I was and with a map that big that's going to be a grind.

Instead I can just boot up my Rocket League and keep trying to make Gold rank. It's mindless and reflex based and doesn't require too much of me.

Now, if I had more hours in the day to game, I'm sure these things wouldn't be a problem. But with barely an hour or two of gaming per day after I work and get all my extracurricular stuff out of the way, that's really what I'm left with at the moment.

And this isn't just Hollow Knight of course. This has always been a thing. Sometimes it's just because a new game comes along that I must play. Final Fantasy XII on the PS2 still calls at me sometimes to finish my file, but once the Wii had come out I never turned on my PS2 again.

There's just way too many games, way too little time, and yet each of us every day is still begging for the next new thing. We are insatiable and no wonder why: we never finish what's on our plate.

-Batman Arkham Asylium: Never understood how to go under Bane to beat him
-Xenoblade Chronicles 2: I was tired being molested by every living creature, even a fly with +30 levels over me
-Doom: the game is about chasing demons but I was mostly hiding and escaping from them
-Majora's Mask
-Ocarina Of Time
-Prototype: Never reached the end, but was very close

Xenoblade Chronicles 2 . 50 hours in. But i havent played in weeks. Will finish it eventually.

Life gets in the way all the time. I just keep playing whenever I possibly can. Oh I only had 30 minutes to game today? Ok then, but I'm not putting this game down till I finish it. During really bad weeks I might just get 10 hours of playtime. But I just keep going. I hate the idea of putting a game down. I'm stubborn. 

Dont usually do it, but these are the ones I can think of

Lord of Shadows 2 - Got to the Carmilla boss and stopped playing afterwards. This game is so goddamn awful and its a shame because the first one was great. I dont think ill give it a second chance.

Hyrule Warriors - Got bored right when Ganon shows up in the main story. Dont think ill be back to it either.

FF13 - I usually drop games when the cast of characters is so horrible, thats why it took me a while to finish FF10, but damn, FF13 is even worse. I did came back to finish it, but ive only finished it once. I usually finish RPGS a couple of times because its my fav genre.

Bravely Default is one that comes to mind, put like 70 hours and it just became like the worst thing ever in the second half of chapters, I did finish that horrible part of repetitive content and absolute stupidity from the main cast, but I never finished the game, I was so done with the game's bullshit, I just dropped it, I'm literally 2 bosses apart from the credits but I'm never going to back to it, been almost 5 years since.

Despite being a FF fan, I rarely choose to beat the game. For example:

FFXII: I got to the last boss, when I realized this was the end I was in too much denial and didn't beat it.
FFXIII: I got to the last boss, the game was so bad that I decided it was not worth any more of my time to beat it. I gave it a fair run, but in the end it was not worth it.