Never Give Up?

The thing I've been pondering today is when/why people make the decision to give up a creative pursuit.

I observe people around me. Some seem to just forge ahead, happily and when the going gets tough, they get going. Some people are full of ideas that never come to fruition, or, they create something and keep it in their basement and no one sees it. Or, they try for something once and never again.

When do you give up??
Why do you give up??