Strong uptrends tend to gather steam as more and more traders flock to the stock. At some point, the bears capitulate and there is a flurry of buying activity which drives the stock much higher. At some point, this massive and exuberant buying exhausts itself, leaving no one interested in buying and everyone interested in selling. This is an obvious reversal pattern when it occurs on extremely high volume. When you see an exhaustion move, it pays to exit the stock and consider shorting it.