I've always said:... the biggest & best bull runs often start by a sudden, fairly sharp period of weakness...
to be followed shortly after by day after day of gains...
my personal theory is that those "in the know" and are expecting great things for a stock (often with deep pockets), will sell off a bunch of shares when they think they can cause a price drop, then they quickly re-buy and get even more, then sit back and watch the profits come rolling in...
nervous sellers just watch from the sidelines in disbelief, saying "I knew that was going to happen............."