I'm afraid I can't help you with that. No explanation. Short, sweet and right on point. It works for me.
I don't start anything with, 'I'm sorry'; that just plays on the whole guilt thing and I save sorry for apologies (it might creep in when I'm having an attack of the sarcastics.. but I try and keep that to a minimum :/ ).
I use 'I' instead of 'You'; to avoid that whole attack/defend dynamic.
Tx