Remember, big losses can begin with small losses.

While it is always possible that the stock will rebound, causing you to sell a good investment, you can help mitigate losses during a bear market with carefully placed stop orders. You are managing your risk. And you will live to invest another day.
No matter which way you think the market is heading, if you own stocks you must know what has to happen to cause you to sell. Sometimes it is a change in the fundamentals, and other times the market reacts in advance to tell you something is wrong. That will be the time to consider managing risk rather than seeking that last nickel of profit.