I'm very particular when I address an envelope. I check and double check the recipient's house and apartment numbers, go over the spelling of the street (and city, if it's unfamiliar) three or four times. I check my own address a couple of times as well - just in case. I place the stamp carefully, squarely in the corner. If the envelope is at all heavy, I add extra postage.
Walking to the mail box, I check the envelope a few more times. Is it sealed? Are all the parts of the address really there? Did I remember postage? I do one (or two) more checks before I slip it in. Once I do, I check to make sure it really got in there and isn't caught halfway.
And then, a moment or a minute or ten minutes or half an hour later, I have a split second panic. Did I put the address?! Did I seal it?? Did I put postage on it!??
Heaven help me - heaven help us all - when I mail the invitations.