Your character isn’t manifest by what you prepare to do. It’s manifest by what you’re not prepared for and how you react to that. Your involuntary reaction shows your character. (paraphrased from John MacArthur, American preacher)
MacArthur goes on to say that it’s the things that catch us off guard and reveal the weakness of our hearts that show who we really are. We can put on a great front when we have time to prepare, but it’s the unexpected that tests our real character.
The integrity of the upright guides them, but the unfaithful are destroyed by their duplicity. (Proverbs 11:3)