The article is about Short Selling. Shorting is although claimed as one of the best financial strategy during bearish market but to me shorting is nothing but a modified form of gambling. I don't consider it to be a pure form of trading.
It is very risky to sell the borrowed asset when one doesn't have adequate capital to repurchase it if the value of asset rise unconventionally. In regular trading, your loss is limited to the extent of your capital. But in short selling, your liability can inflate to infinity!