You don’t owe an explanation for changing your number, your major or your mind.

A reason, once you hand it over, becomes something to argue with. That is why the request for one often feels less like curiosity and more like a hearing. What you study, who can reach you, and what you now believe are yours to settle while you are still in the middle of working them out. Changing your mind is usually evidence that you were paying attention.

Pick one decision people keep asking you to defend. Write the shortest true sentence about it, something close to, I changed it, and practice stopping there. The pause afterward is less awkward than the paragraph you were going to fill it with.