investors purchase a stock when they believe that it is undervalued and sell when they feel it is overvalued

Answer: True

Explanation:

You did not write down the question that are you asking and that is considering this sentence. Since I could not find it on the internet, I only found that it might be True or False question.

This statement is true. In that way, If the stock gets overvalued over time and they have the opportunity to sell it, the investment was successfully done. If this sentence or statement is considering correctness I would say that everything is written correctly except indefinite article in ''a stock'' because there shouldn't be an indefinite article, only the word ''stock''.