The most dangerous question you can ever ask yourself when playing a game is...
"Why am I doing this?"
I've lost track of how many games I've dropped simply because I came to some sort of realization about the "why."
The "why" is a huge part for me.
Why am I leveling?
Why am I going after this loot?
Why do I plant these crops and water them every few hours?
Why do I decorate my house?
Whenever I ask myself why I'm doing something, if the game isn't giving me a really good reason to keep doing it then I'll probably stop. That's dangerous when that thing I'm doing happens to be the main reason I'm playing.
For example, in my farming game called "Farm Together" there's a lot of chore work. I played that game every day for a month. I planted crops, flowers, decorated my farm and house, did all the in-game chores for the gems, etc. I just kept doing it because that's how the game is played. After a while, I asked myself, "Why am I doing this?" It was then I realized I really didn't have any more rewards to earn or levels to gain. I was just doing it... because. Now I haven't played in a week and I don't miss it.
There's no 'right' or 'wrong' reason for doing something. It's entirely a subjective thing. "Because I'm having fun doing it," is a perfectly valid response. But most of the time when I stop to ask myself that question, it's because there's already a problem -- it's probably because the fun stopped.
Asking the 'why' question is also a good exercise when evaluating a game's design. If you're a geek and a masochist like me, you start to dissect the systems in a game. Why are the devs wanting me to do this thing in this way? Why was the decision made for this mechanic to be here? I like those questions.
Give it a try sometime, though I warn you it may ruin a seemingly perfectly good game.