It just happened to me yesterday. I dropped an egg at 18 days that was under a broody and I was candling them. Fully formed little chick, I too was/am devestated and I feel awful.
i am so sorry, i just learned how to candle this summer i checked on a certain egg it was alive and kicking but i checked it to much and killed it , when i went to check on it again nothing. so i put it back and said to my self no more the other eggs hatched not this one. my prayers are with you
It's true, it does happen to all of us. It's just part of incubating. I felt terrible one time for getting rid of an egg too soon and it had a little baby in it! I candled it and thought for sure if was not viable. We all have our moments, but that will be just a memory when the little babies arrive. Best of luck on the rest!