Definition of shorting according to Investopedia.com

The selling of a security that the seller does not own, or any sale that is completed by the delivery of a security borrowed by the seller. Short sellers assume that they will be able to buy the stock at a lower amount than the price at which they sold short.

Yes, some individuals are successful

Bill Ackman comes to mind as a successful short. Im pretty sure there are other individuals who have successfully shorted stocks for a living and will continue to do so.

Logic

I might not be the smartest men alive, but logic is the main reason I avoid shorting. Here it goes:

If I short a stock, my biggest gain will be 100%  and my biggest loss could be limitless (assuming I do not get a margin call). On the other hand, if I buy a stock, my gain could be infinity, while my downside is limited to losing my intial investment or 100%. Now that’s what I call controlling my risk/reward.

An example:

On January 2007, David Dreman wrote an article for Forbes properly titled “Short The Exchanges“, in which David Dreman considered the stock exchanges (CME,ICE,NYX). At the time of writing, Chicago Mercantile Exchange Holdings (CME) traded at $530. The stock continued its unprecedented run up to $714. The stock is well off its highs, but an individual would have had to stomach a 35% increase in CME’s stock price.