The hardest decision for investors is when to sell their stock. Investors tend to hold onto a loser, hoping the stock will bounce back and they can avoid the pain of regret, according to experts. And when investors sell a winner they are upset for selling it when the stock goes higher.

Experts recommend buying quality stocks and holding them for the long-term. But that doesn't mean investors can be complacent.

So, how do you know when to sell a stock? The easy answer is when you need the money. Other circumstances that could force this decision include a fundamental change in the company's financial health or competitive position.