Never concede unless you know for sure it's truly over.
Truth. A warlock was down to 9 health had a giant shield and 3 other giant creatures posed to finish me off and All I had was 2 armor smiths, a now silenced acolyte of pain and a 2/2. Draw Grom, run my 1/2 silenced Acolyte of Pain, Execute the giant, grom, shield slam my Grom, win the game.
He must have been piiiiiiiissed.