That's why the White Walker King failed to kill Jon Snow. He only had 13 good men.
20 is the magic number, you see.
EDIT: Seriously though, the point is that Stannis, considered the best commander in Westeros (stated by multiple characters in the show, while in the books he is widely underestimated, even by Jon) commits the mistake of leaving his already dwindling supplies unprotected as if this was his first time marching into battle. The use of plot device after plot device as an excuse for characters doing the unthinkable and acting against how the show itself previously portrayed them is what pissed me the most. I mean, most theories about the battle of Winterfell have him using the frozen rivers to his advantage, and Theon's WoW chapter gives us a hint that it will probably happen. Someone who is NOT from the North use the ice and snow to his advantage says a LOT about his adaptability and knowledge of terrain... But in the show 20 good men machina can do anything, while a shirtless Ramsay double wielding swords can butcher the best killers of the Iron Islands.
Stannis might end up burning his daughter, but I assure it will take MUCH more than 20 good men to push him into doing that. People who say he would've burned Edric forget that if he really wanted to he would have tortured Davos for his location... But what did he do? He thanked his Onion Knight and left Edric alone, for he wouldn't be forced to choose anymore.