Darnell Furlong admits West Brom's players were floored by their late defeat to Newcastle United.
Former West Brom loanees Jacob Murphy and Dwight Gayle combined eight minutes from time to hand the Magpies their second straight league victory.
Furlong told the club's website: “Once we scored I thought we were going to go on and get a win because we were the better team for much of that second half.
“The boys are devastated. We didn't start well enough but then we showed what we were about in the second half and came out fighting.
“We've played well in a lot of our recent games and have been in and around it, but it's those fine margins which decide the game sometimes.
“We can take positives out of the performance and the confidence is there, but we just need to cut those little errors out now."