A fence runs around the whole yard without moving an inch. Boundaries work while you sleep.

A limit you set once keeps working without you having to defend it every time. That is the whole point. You decide in advance, and the decision does the work when you are tired, or outnumbered, or caught off guard. Arguing your way out of something in the moment is exhausting, and the moment is the worst possible time to be deciding.

Decide one thing ahead of time this week. Phone off at eleven, no lending money you cannot lose, no rearranging weekend plans by text at midnight. Say it once to the people it affects so you do not have to say it again each time.