It is very rare that the averages can sustain an endlessly bullish move, and Jim Cramer says rallies only end in two ways: with a big ugly decline or if stocks become exhausted.
"Let's stay vigilant. Take off some obvious gains, because no one ever got hurt taking a profit. But then let the rest ride, wagering that if the market really gets hit, the buyers who have been patiently waiting will finally decide to pull the trigger," the "Mad Money" host said.
The question on Cramer's mind is how will the hot streak come to an end?
Cramer frequently refers to the Standard & Poor's proprietary short-range oscillator to take the pulse of the market. Typically the short-range oscillator stays within five points of zero, which is neutral. When it goes over five, Cramer becomes nervous.
On Tuesday night, the oscillator hit 10. It indicated a level of danger to Cramer, that stocks are severely overbought.
"When it goes over 10, I get downright fearful because when the market looks so great, like it has lately, you tend to be the least prepared for a big decline," Cramer said.