Why is selling stocks short a high risk investment technique

Short selling stocks is a high risk technique as you are betting that a stock will go down in value and the downside risk is essentially unlimited.  When you buy a stock "long" you know the stock can "only" go to (0) so your risk is what you invested, when you are selling a stock "short" the stock has no limit to far it can go up and therefore how much money you can lose.