While I was in a flight, I watched the movie about investors who foresaw the subprime mortgage crisis in 2007/2008. This reminded me of the atmosphere of the time when I first joined the sector. 

One said something like "Many people don't think too much about the worst situation, and we use that human weakness to make the profit." The short sellers sincerely looked at numbers of mortgage loans of the U.S., and based on the analysis they concluded that this is a time-bomb and would burst soon. 

The remark is worth hearing. We human beings seldom think about the worst cases that we may face in the future, because thinking about bad situations is itself painful. Thus, we always are hit by the terrible situation because we do see the facts telling us the horrible future but deny the very existence.

Following the other's opinion to see the market is not a smart answer, because truth is not voting but fact and reason. That said, the movie also shows us how the short selling requires courage. If you make long investment only, your loss will never be below 0, but when it comes to short, theoretically the loss can be infinite negative. Even when we're in a bubble, we cannot foresee exactly when it will burst.