The answer you assumed is not always the answer somebody agreed to give.

Silence and vagueness get filed as agreement, especially when the answer you wanted is the one available. Someone says they will try, or nods while thinking about something else, and you leave holding a commitment they never made and cannot recall giving. The gap shows up later, when it looks like they let you down.

Before relying on an answer, say it back in specific terms: this thing, by this day, done by you. Ask directly whether that is a yes. Written confirmation is not distrust; it is how two people discover they were picturing different arrangements.