I think the childhood aspirations, particularly the whiz kid one, are near impossible on a normal life span with aging on. I have yet to successfully complete that one, and the closest I came to it was with the child going two nights without sleep burning through potions.
The "A" in school for children requiring level 4 in 4 skills is a big hurdle for me. They can level social and either creative or mental no problem, but motor seems to be hard to level in tandem with other skills.
Chess game win requirements can also be frustrating. On public lots, sims crowd them, and then everyone starts talking. That slows the play time to a crawl, and all it takes is one random sim being a jerk to show up and put everyone in a poor mood. There's also the chance that after you've invested 3-4 sim hours in a game, the opponent will get hungry or need the bathroom and just leave, making all that time wasted. In your own home, the risk is a bit less, but you need to have a sim that has the free time to play chess with your sim. You can invite someone over, but without them being under your control, you can't make them stay put.