Buy low, sell high is a sure way to make money, but how many people can really buy low and sell high?A good time to buy a stock usually is when there is a broad market sell off, which drags the stock down. Another possible good time to buy is when certain news affects the stock price, but actually has no impact on the company's financial performance. One good example was the short report on Enphase in 2018 and 2020 where the stock fell more than 20% in a single night. It was a good opportunity to buy in on those days.A good time to sell a stock is when the fundementals of the company has changed. Slowing growth, losing market share or changing business models are some examples of this. Another good reason to sell would be if you have found a better investment opportunity to place your money into.