This afternoon the U.S. stock market went bananas and I decided to sit down in front of the television, watch, and enjoy myself. When the entire market is run mostly by computers, not only can traders control the minute by minute action but they can even set the computer up so that once certain price levels are reached, their trades get executed automatically, so actual human action is not even necessary. What happens when the computers are overloaded or someone makes a mistake? Well, watch this short segment from CNBC and see how the Dow Jones can drop 500 points and then make it all back in less than five minutes.

This is why many people think short-term trading in the market is nothing more than gambling. Literally anything can happen on any single day, in a single hour or minute, or in this case, a few seconds. Market watchers will tell you to use limit orders as a way to specify your exact desired buy and sell prices to avoid getting taken to the cleaners when markets react violently like this.

The problem with that, of course, is that your order may hit in a moment of panic, and had you known that was happening, you never would have made the trade. Imagine if you came home today to learn that you sold 100 shares of Proctor and Gamble at $50 (a limit order you had set) because it traded there for a brief second based on computer malfunction, but rebounded to $61 within seconds. You would be furious. Limit orders are not always the answer. Investors, especially those who are novices, need to be very careful. As we saw today, the market can be a landmine.