I found out today that not one, not two, but FIVE envelopes from a stack of about 60 invitations to a faculty member's retirement party were sent out, by me alone, completely empty. I think I got into absent-minded "stuff/lick/label/stamp" mode that I forgot to insert anything into some of the envelopes. Luckily all the recipients were family members, and they knew about the party anyway. I did feel bad for the wasted stamps, which just went up in price. (Aside: there are now 'Forever' stamps, which are supposed to be good 'forever', no matter what the price of postage is. I don't believe this one tiny bit!)
It just goes to show, if you pay a guy 7 dollars an hour to sit in a hot closet measuring 6' x 5' with no windows, no air circulation, and all-you-can-watch YouTube, this is the quality of product you may receive.