As Dean gets older, he starts to learn what death means, and that most people can not do it and come back, and so he decides not to do it.
Until Sam just had to loose his shoe in the middle of a frozen lake in December.
Is a shoe really worth it? No. But Sam was crying about how those kids threw it there and its not like they had money to buy a new pair, and maybe the ice was thick enough to be safe?
Nope. Dean fell through and Sam screamed.
He didn't die right then, he managed to get out and give Sam his and get back to the motel.
Then he promptly "fell asleep" as he told Sam.
Man the things he does for that stupid kid.