Wanderers took an early lead against Nottingham Forest at Molineux on Saturday only to see the visitors turn matters around to triumph 2-1 thanks to former midfielder Adlene Guedioura's winner.
It extended Wolves' winless run to eight games, with four defeats in their last five games, a sequence of results which has seen them slip from third place in the Championship to 17th.
Solbakken said: "After conceding the second goal (against Forest) we looked like a team who had not won for a while.
"You could see that in the way that we passed the ball. Safe balls went wrong and many players made the wrong decision.
"That is often down to a lack of self-belief and that has to go before we play Millwall on Tuesday. We have not lacked it before but you could see it after we went 2-1 down. We have to work on that because if you are afraid of something you will never turn the corner."