Amaziah, the priest of the false shrine at Bethel, demanded that Amos stop prophesying.

14    Then Amos answered, and said to Amaziah: " I was no prophet, Nor was I a son of a prophet, But I was a sheepbreeder And a tender of sycamore fruit.
15     Then the LORD took me as I followed the flock, And the LORD said to me, ' Go, prophesy to My people Israel.'

I have seen Christians defend their unsuccessful use of power by citing their education and accomplishments. Actually, their education was often based on misunderstanding of Scripture, and their past success is a lot less than they admit.

Amos had a clear, rock solid call from God to do what he did. A spiritual weakling, a confused saint, or a misguided "legend in his own mind" cannot be a prophet.