"It is difficult to explain," he told L'Equipe.
"But when we create many chances, we shoot 29 times and we only score once, then it is hard to accept.
"We knew we were better than Rosenborg. We dominated the match, did everything required to win, but lacked luck.
"We play well, dominate the games, create chances, but don't manage to score. It is all about little things.
"We lack confidence and need a lucky goal. It could launch the machine.
"Of course we doubt. But it didn't happen overnight. It has been our problem since the beginning of the season. We also concede too many goals. We are in danger from free-kicks, more than in the previous years."