Of the six people I routinely play with, one of them gets discouraged when he feels like his character is not making much of a difference in an encounter.
Part of that problem is right now the game is a form of escapism from a difficult time for this player. He works all day on a hard newer job, he has few friends near where he lives (which he moved to relatively recently, away from his lifelong friends), and then in the evenings he is taking care of a newborn who is fussy lately. Taking care of a newborn in the best of times is difficult, and it's even more so when they're teething or sick. Bottom line, his life is a bit rough and he uses D&D online with his friends as a form of brief escapism, playing the role of this hero doing good and making things happen in a fantasy world.
So in those brief breaks when he gets to play and engage in that escapism, he wants to feel like he's making a meaningful impact on what's going on. If he's going to escape into the role of a hero doing good - he wants his hero to be heroic and actually doing the good.
So if he just wiffs multiple times in a row, or if his character is paralyzed for an entire battle, I can hear him getting discouraged. To him, the little time he had to try and escape into the fantasy of the game left him as frustrated as real life.
That issue wasn't as prominent for that player when we were playing live, and he didn't have a newborn. But right now, it's having an impact. So it might be in his best interest to play a character that is more likely to have an impact on the encounter throughout the encounter. Even if that means his average damage goes down, or his defense goes down, I think he'd be happier if he felt like his character was "doing something" every round.