Jeremiah 20:9 Then I said, I will not make mention of him, nor speak any more in his name. But his word was in mine heart as a burning fire shut up in my bones, and I was weary with forbearing, and I could not stay.
When God calls someone to issue a warning (or warnings) on His behalf, it is hard, and sometimes there are painful consequences from the disobedient whom we warn. There's a strong temptation to be like Jonah. Or like John Mark who left Paul's team and went back.