So, work and life in general have been very stressful for the past two months, and today I when I sat down to register postcards, I saw it didn’t have an address on it. I looked closer, and it was postmarked on April 8, 2024 from my town. The ID is US-10301899.
Turns out, I wrote, put my small return address label on it, stamped and sent the card without addressing it! USPS thought it was for me and delivered it to me.
Tomorrow, it goes back in the mail to California.
Haha, happens to best of us. At least it was delivered back to you 
I have put an extra 25 cent stamp that was not needed. I have once put 2 cents too little - and the sorting girls were so kind that they put on the missing stamps, only covered the ID number, and I later got a reprimand for that from the administration. (Now there is no sorting at the Gulbene post office, everything is sorted in Riga. If I stick too little again, the card will not go.)
That’s all, the pure stuff. But nothing major has happened.
I once put a card in the mailbox without a stamp. I sent another one afterwards, because I waited an hour for the postman to empty the box (it said it would be emptied around that time) but no one was coming.
I wasn’t paying attention, put international postage on a domestic envelope.
I had some extra meetup postcards signed at a meetup.
On my way home, I decided to mail the other postcards, and without checking I mailed all the postcards, also the extra ones with no text, no address and no stamps.
I guess those postcards ended up in the bin.
Not Postcrossing, but once I mixed up the field for sender and recipient on a parcel - I was very happy and surprised until I realized I sent myself that parcel 
I can’t tell you how many times I’ve done this, as well!
Oh no!!
Lol
Mine is more embarrassing … I got a nice card, but it took me forever to decipher the handwriting… I managed the ID number after a while, but read the name totally wrong… I then proceeded to send a hurrah message with the name I thought I had figured out. Needless to say, it was not even close to the sender’s real name. I did send a second private message and apologized profusely… to never hear back.
I’ve done the same thing. So embarrassing! Now if I can’t figure out the name I’ll sent my thank you note addressed “Hello postcrossing friend.” Not as personal as I like but not embarrassing either.
Been there, done that 
It’s almost worth it to skip the original hurrah, go read the profile of the sender and come back fully armed with the correct name.
I just straight up never use names on my Hurray messages for this reason. I’m always so worried I’ll get the name wrong somehow, even when it’s clear. So I just start off with “Hello and thank you!” and then will say something to respond to what they had wrote or something about the card itself so that the person knows I actually read/looked at the card!
But I think my silliest mistake was simply not sending a card! I had requested a few addresses at one time so I could sit down and do a bunch all at once but somehow I missed one of the cards. A few months later and it became expired. I clicked on it to see where it had gotten off to and I could not recall seeing that person’s bio at all and had not sent a card! So I quickly sent off a “new” one and pretended that it had gotten lost in the mail lol
I don’t use names either, most recipients get “Greetings from Florida!” as the opening line.
So relatable- I usually type out a few possible names and then backspace to just “Hi!”
My most recent mistake was finding cards that were ready to post being flattened between books from two months ago 
…
Whoops 
!
