I cannot think of a single reason to agree with that idea.

I can't think of a single reason not to tell her.

He could not think of a single reason why they would want him dead.

If for any single reason, it means more women will take interest.

Because they've never given me a single reason not to.

Son, I can't think of a single reason to say no.

And neither could I think of a single reason not to.

He couldn't think of a single reason why her opinion should matter to him, but it did.

Indeed, there wasn't a single good reason that she should not be part of the mission.

"Can you tell me a single good reason why not?"