It's important to always have intent and purpose everytime you step into that batter's box, but some players get apprehensive and doubtful. Get your players to become confident hitters, instead of swingers, with this "Yes, yes, yes" drill.
We are all aware umpires don't make the best calls sometimes. However, they are the ones making the decisions on balls and strikes, not our hitters. Therefore, hitters should always be thinking "yes" as the pitcher winds up and releases. If hitters train themselves to think "no", and then disagree with the umpire when a strike is called, they will get comfortable being passive and reactive hitters, instead of confident hitters.
When this confidence is displayed in hitters, it becomes apparent in you as a coach. You no longer become a cheerleader and hoping your team gets hits. You will start knowing your team will get hits.