There are lots of challenges people do because they enjoy it. Things like trying to complete the community centre in year 1, which requires using each day to its fullest. But it's all self imposed.

There are probably only two things that could kind of be considered, which I will try to keep spoilers to a minimum for any readers but it's still a little spoilery. One is what happens at the end of year 2, but if you don't stack up then you can retrigger this on demand. And the other is the randomised quests that come late game with time limits, but this is a short term time limit (do X in X days) and you don't have to do them they are just random challenges.