Translation:Come on! You need to be confident!
It's actually far more accurate to say "have confidence" as the Chinese character 有 means 'to have'. I have no idea why they put "be" there in the translation, there is no 'being' verb in the Chinese statement at all, and saying "have confidence" is the obvious choice for an English answer.
Two years later and, "Come on! You need to have confidence.", is still being marked wrong. I've reported it.
Duolingo clearly doesn't have a problem with people using the turn of phrase "have confidence" instead of "be confident" since the next question literally insists upon it:
Sentence: 一个医生应该有信心。 Accepted Translation: A doctor should have confidence.