I've been waiting for hours at that shop, but the meal still hasn't come out.

Do you understand the necessity of this project?

That information is unnecessary.

That information is completely unnecessary.

He thinks that war is a necessary evil.

That unsolved problem keeps him awake at night.

That unsolved case keeps him awake at night.

The process of name resolution is very important in computer networks.

No problem, I will do that job.

That proposal is completely unthinkable.