Why does it take a disaster for us to learn from an event?

As an example, take Japan's current nuclear disaster. I hope it won't become a monumental disaster but I am doubtful they will manage to stop it. Suppose our wishes are answered and they will contain the situation, then many people will say: "You see, even in such an extreme case a nuclear disaster was averted, so there is nothing to fear and let's continue with nuclear power." On the other hand, if this will develop into a catastrophic event, people will be much more fearful of nuclear power. Why do we need the catastrophic even in order to learn? Isn't the strong possibility of what could go wrong show us enough to be weary?

In sports it is known that a team doesn't learn as much from games they win as from games they lose. Even if the whole difference was a lucky shot by either team at the last second to win the game. It's basic human psychology.

Why are we built like this? Shouldn't we be able to learn from seeing a mere possibility?
While in sports there are always more games (or almost always) nuclear events don't happen daily and we can ill afford new test cases (for example, there is a hazardous nuclear reactor within less than 50 miles of NY.)  I'm not trying to speak against nuclear power, as this is a different, and very interesting, discussion, but to try to understand a basic question of human psychology. Though I do also want to warn that we should learn from this event as if the worst case scenario (which no one seems to  even be able to imagine what that would be) has already happened, as whether they will miraculously save the situation is not something we can expect in the future..

Why can't we learn from seeing options as well as from seeing actuality?