Sign No. 5: herd mentality
People can walk on the moon, but following the herd is still irresistible.
"There are a lot of group or herd behaviors where people follow others they believe know what they are doing. Those people don't actually know what they're doing," says Mansharamani.
By the time you realize everyone is falling off the cliff, it may be too late to scramble to safety.
"The classic story that you hear people say -- if the valets and waiters and all the service people around the rich hotels can think of nothing other than what stock to buy, it's probably time to sell," says Rodriguez.
It doesn't help that bubbles often come with compelling stories that can cloud facts, even for the most clear-eyed contrarians.
"It's like in the heyday of the Internet stocks. The narrative was it doesn't matter that they don't have profits now -- they will and don't be late to the party. So it's usually that which gets you," Rodriguez says.