When did you sell stocks?

If you know anything about stock investment and stock market, you may have heard of "buy low buy high sell". This basically means that if you want to make money in the stock market, you have to buy a stock at a low price and then sell a higher price. This is a basic principle that only makes sense. Unless you are short selling, you have to buy a stock higher than the price you buy to earn capital gains.

It sounds easy, right? Well, once you try to put it into action, you will fall into some roadblocks. How do you know the stock is low enough to buy or is it high enough to sell? Investment professionals always tell you that you can not predict the stock market, then how do i know that I am selling at the right price?