Courtois was speaking ahead of Belgium's opening game against Panama, before fixtures against Tunisia and England.
"I think we have the quality and talent. We have a group of players who know each other very well and most of us are in good form," he said.
"We feel confident but I wouldn't call us the big, big favourite. I think we are outsiders to win. We have a chance to go far and we have to believe.
"We are not going to say that we will win or that we are the best team. We have the quality to go far and we believe in ourselves. Belief is the beginning of everything."