The person allowed to reconsider can offer a more honest yes.

Agreement means very little when refusal was not really available. A yes from someone who cannot back out later is a yes about the pressure in the room, not about the thing being asked. Leaving the door open costs you the illusion of certainty and buys you an answer you can rely on. People say what they mean far more often when saying otherwise would not be a scene.

Add one sentence when you ask for something this week: tell the person they can change their mind later. Then make it painless the first time somebody does.