However, any kind of shorting strategy involves not just an expectation that the market will go down some time in the future but instead requires that you say exactly when.

Especially, if the stock that you are short begins rises, you may be forced to buy back the stock you've sold - the traditional "short squeeze". http://wiki.fool.com/Short_squeeze

Basically, playing to a down market is inherently harder than playing to an up market. It can be done but it is harder. Just another way the video is full-of-shit as many folks have mentioned.