How do we know when to quit?

A young student recently asked me the following question: How do I know it is time to quit something and when to persist with it? Here is how I answered the question: There is no one answer that fits everyone. There are many ways to figure this out. For me, the best way is to go back to the reason why I started something. If the reason I started something is still relevant and important, I know that I would like to continue to engage on this topic. Then the next question to ask is if the activit...