Either one or both works.
Mine is completing the Pokedex in the original Pokemon games. All you get is just Professor Oak giving you a wink and a small few second cut scene. And a congratulations text. Imagine spending all of your time then, getting all 151 and even 252 pokemon just for that? Yeah no thanks, I never completed the pokedex.
Going the Joja-Route in Stardew Valley. I say this mainly because, it is what you make of it. You forfeit being able to complete the Community Center by earning things, when you sign your soul away to Joja. What I would’ve liked is seeing Pierre go out of business completely. I just think that would add a route of depth in the game where you have to make ends meet through Joja because Pierre is permanently closed.
But, that doesn’t happen, he’ll still be in business despite his depression about Joja running things. Kindof ruins the whole concept of doing it for the achievements even.
I draw the line at whether it’s something that can be done naturally, as a result of playing the game and enjoying it enough to put in that much time. I’ll entertain trying to 100% a game that has an achievement to farm 1000 of some herb, if it’s something that I’ll just come across in due time by making full use of all the game mechanics, and presumably see some form of in-game payoff for my efforts. I’ll instantly become content with just seeing the credits if an achievement to get a similar quantity of something is just an excuse to pad play time by making me grind some monster drops just for the sake of getting that last achievement.