We all need to believe that our lives are worth living.

You're the part of me I need to believe in.

People need to believe something whether you want them to or not.

They needed to believe in him now, and he played upon that.

She just needed him to believe a little, to give her something to hold on to for the time they had left.

He did not need to believe anything, and could see things the way they were.

He needed to believe that she was waiting for him.

People only need to believe for a few minutes at a time.

You need to believe that these are sound, even if other people don't like them.

On the other hand, one needed to believe in something.