Profit Taking
  
You bought a thousand shares at $8 and now the stock is at $73. Hugely good call for a 3-year stint. And now the stock is dropping from $73 to $71 and, just like everyone else, you're going to do your own profit taking here in selling your shares at $71.
When you profit-take, you've profited from an investment, and now you're turning it into cash.