We were living in San Diego when I wrote my first two manuscripts. When I finished the first one, proofed it about a bajillion times and was finally ready to mail it, I took it across the street to the shopping mall, which had a post office in the basement, went inside and got postage, then took it back upstairs and dropped it in the box.
See, I was a regular at that post office and the clerk knew both me and the kiddo by name. If I'd changed my mind about mailing it and went back inside to ask him to give it back, I knew he would. But the mailbox outside was picked up by strangers, and I didn't think the odds were as good about them giving it back to me.
Trust me -- I would have tried.