Besides the fact that the market is turning sour, I sold AB because of several factors.
First, AB has been getting more press lately. This used to be a quiet little stock that nobody paid attention too. Now I keep reading about how this is a great place to put your money if you want to play the world markets. With higher visibility comes higher expectations and the way the market has been selling the news I didn't want to be on board during earnings (Jan 24). Last quarter AB reported blah numbers and the stock didn't budge. Since then, the stock has really ramped up and is now poised for a pullback.
Also, the chart shows some signs of churning. This is when an above average amount of volume is accompanied by little or no price movement. This shows that the institutions are exiting.
The bottom line is that I rode AB up for a 23% gain. Might as well get out while the gettin's good.