Oh Lordy, have I been there! And I don't think this is going to be of any help, but. I think an explanation has valid logic behind it, and an excuse has made-up logic behind it. And most of the time, the judging of what's valid and what isn't is ENTIRELY subjective!
CK, I believe you've had a fair amount of experience with ...you know what! What do say to Rous.' query? (Good luck, by the way, Rous.--perhaps you'd better take a quick course in persuasion techniques? )