Barca must overcome a 4-0 deficit to reach the final.
Pique said: "I know the result makes it hard to believe. This Wednesday we all must to have the faith of a child and lose our common sense. If we go into the match with that mentality, maybe we can do it, even if common sense tells us it's complicated.
"The only team that can fight back from a 4-0 deficit against this Bayern Munich is this Barça. We need to be ourselves, we can't feel as though we've already been eliminated. An early goal would give us a lot of confidence," said the Blaugrana, who added: "we're part of a Club that has a lot of history and we'll do our best to add to that history."