What counting to three is actually doing
Counting to three is the most widely used and least explained technique in parenting. Most adults inherit it without being told what it does.
It buys time. A child asked to stop doing something needs a few seconds to disengage — to put down what is in their hands, abandon the plan they were mid-way through, and switch. The count supplies exactly that, with a predictable end.
The predictability matters more than the number. A child who knows the count always ends the same way can use the interval; a child whose adult sometimes reaches three and sometimes reaches five cannot, and will test where the real edge is.
If nothing happens at three, you are not counting. You are warning repeatedly.
It also fails in a specific situation worth naming: a child in genuine distress is not delaying, and counting at them adds pressure to a system that is already overloaded. The technique belongs to reluctance, not to panic.