Three. The other adult, and four. The audience

If there is a second parent, most shouting sits in the gap between two different standards. One says shoes now, the other says leave him, and the child, entirely reasonably, waits to see who wins. Volume is what the losing adult reaches for.

You cannot fix that during a morning, and trying is the argument you always have. It gets fixed on a Sunday, in a conversation with no children in it, about one behaviour rather than about parenting.

The audience is the other one. Almost everyone shouts more when they are being watched, especially by their own parents or their in laws, because at that moment the shouting is not aimed at the child at all. It is a performance of being in control of them, for somebody whose opinion still gets under your skin. Knowing that is most of the way to it happening less.