One has to be confident in himself.

一个人一定要对自己有信心。

You must be confident in what you do.

你必须对所做的事有信心。

Carrick also appears to be confident in his ability.

卡里克也对他的能力很有信心。

Be confident in who you are and value what you're doing.

对自己以及自己正在做的事保持自信。

Be confident in your judgment and believe in yourself to get things right.

要对自己的判断有信心，相信自己可以做好事情。