Why the number has to be said out loud

Most families never state a figure. The parent worries that naming a limit will look like a lack of belief in their child, so the conversation stays vague — "we will manage", "we will see" — right up until an offer arrives and the vagueness collapses into a no.

That is the worst possible moment for it. By then the child has built a year of plans on a number nobody ever gave them, and the refusal reads as a verdict on them rather than a fact about the household. A constraint given at the start is a useful part of the design. The same constraint revealed at the end is a betrayal, even though it was true the whole time.