Over-explaining usually means you’re arguing with yourself, not with them.

When you keep adding reasons after somebody has already agreed, the extra reasons are not for them. They are for the part of you that has not finished deciding you were allowed to ask. Over-explaining also tells the listener you expected a fight, which can quietly produce one that was never there. The length of a justification tracks your own doubt more than their resistance.

Notice where your next explanation stops being information and turns into defence, and stop it there. Say the thing, give one reason, finish. If the doubt is still loud afterwards, that is worth looking at on its own.