The people of Nineveh listened, and trusted God. They proclaimed a citywide fast and dressed in burlap to show their repentance. Everyone did it—rich and poor, famous and obscure, leaders and followers. Jonah 3: 5 (MSG)
If I were Jonah, I would have been a bit cynical as I started preaching in the streets of Nineveh. I would have expected people to laugh at me, reject me, and hurt me. The last thing I would have expected was for the people to actually listen and repent. Jonah's story is a great reminder that you never know how and when people will respond to God's Message. You can only proclaim, you can't predict.
I've been preaching and teaching for many, many years. I've delivered messages that I'd crafted with care, only to feel my words die as they left my lips. The message seemed to fall on deaf ears. I've also experienced times when the simplest message spoken without preparation becomes like the falling pebble that starts an avalanche. You just don't know how your words will be received.
Somewhere along the line, every wise teacher, parent, preacher, and employer learns that you can't make someone listen. You can't anticipate or control the effect your words will have on your hearer. You can only speak the truth, love, let it go, and leave the rest to God.