A non-doer is very often a critic-that is, someone who sits back and watches doers, and then waxes philosophically about how the doers are doing. It's easy to be a critic, but being a doer requires effort, risk, and change.
The difference between school and life? In school, you're taught a lesson and then given a test. In life, you're given a test that teaches you a lesson. Tom Bodett