I recall reading (One of Tyler Cowen's books, I think) that happiness is highly correlated with capacity for self-deception. In this case, positive / negative events would have little impact, but not necessarily because people accepted them, but more because the human brain is a highly efficient self-deception machine.

Similarly, a tendency toward depression correlated with an ability to make more realistic predictions about one's life. So I think it may in fact be a particular aspect of human psychology that encourages self-deception and responds negatively to reality.

None of this is to say that these effects can't be reduced or eliminated through various mental techniques, but I don't think it's sufficient to just assert it as cultural.

It's said that "ignorance is bliss", but that doesn't mean knowledge is misery!

That's a pretty good line!