Actually, you won't be able to do certain activities if you're not famous enough. Each rank unlocks a new activity. The early ones like print ads and jingles have no minigame: they're mostly based on your sim's mood, luck, and possibly skill points.
Once you reach two stars, the activities will have minigames, but your sim will refuse if their mood is too low. Yes, you have three guesses, but the sequence is the same each time. So if the director likes a certain tone in a certain order, you keep doing that while changing what he doesn't like. It's possible to get a 100% success rate in these, although it gets repetitive after a while. Although the faster you get it right, the more you're paid.
Once you reach a certain level, you'll only have two guesses, but you only need to get 2/3 right. If you're unlucky, you could fail, but it's not that often
So yes, there's some luck involved, but there's a strategy to it
(This is about The Sims 1 Superstar btw)