"It is so disappointing that we can't create the kind of confidence with winning games. One defeat seems to spoil all we have and then we have to start again," said the Dutchman.
"We still have hope and faith that we can get fourth place, but it will be harder in every game. It was going to be difficult even before Wigan.
"We know we needed to get three points and that's why the disappointment is so big because we failed.
"We have made it really difficult for ourselves now, but we have an important game on Thursday and must be ready for that. We can't be disappointed too long."