You don't punish a fish by throwing it into water.
What it means
If you are to punish someone, the action you prescribe for them as punitive should not be a positive reinforcement. The punishment must sting the person in some way, otherwise the person would not learn from their mistakes.
This proverb is applicable to unjust politicians, for example, who would reward members of their cabinet they like even when those members fail to perform well.
