What this really means is that educated traders do better . . . Due to the extended bull market, shorting has recently been primarily a shorter-term strategy, although you can hold a short position for as long as you wish. When bad news or sector rotation takes a stock out of favor, the company and brokers do everything in their power to buoy the stock. Most investors want the market to move higher and they invest in the hopes that individual stock prices will go higher as well. Only shorters hope that stock prices drop and shorters are few in number.
Companies release positive news stories and brokers do their infamous upgrades.
These actions become forces that tend to drive the price back up in an up market. In a bear market, it doesn't matter what brokers or companies say, it rarely has power to drive stock prices back up for the long-term. Well, the truth is that shorting generally takes place without the stockholder's knowledge. Under certain conditions stockholders can instruct a broker not to allow their shares to be shorted, but this is rarely done. Because they make commissions on the deal that actually work out better than in a normal transaction.