You are presented with evidence of a possible global catastrophe in a few hours. You can do one of two things:
1) Quit what you're doing, go eat a pizza or something for your last hours alive. Maybe spend it with your loved ones.
2) Take advantage of the panic to make a profit.
Now, there are two possibilities here, resulting in four outcomes: a) the world ends, b) the world doesn't end.
1a) You're dead. Who cares?
2a) You're dead. Who cares?
1b) You had some pizza, kissed your kids, but hope they don't want to go to college 'cause you're broke.
2b) I'M RICH, BITCH!
So option 1 has outcome of x% dead, y% poor. Option 2 has outcome of x% dead, y% rich. Clearly, option 2 is the better solution.
(Yes, I know many will opt for option 1 anyway, particularly the "spend time with family" part. These people don't work on Wall Street.)