Grab a couple of dice. Roll them.
If you get below 5, those are rookie numbers. Shout at the dice, let them know they're underperforming.
If you get above 9, that's what we want to see! They're good dice, and you should acknowledge that.
Repeat that and keep a record. You'll notice that negative feedback often results in better performance on the next roll. Positive feedback, conversely, can make them get lazy.
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