Unknowns

There are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns – the ones we don't know we don't know.

It was all like a single equation with two unknowns.

Life is full of unknowns.

There are definitely a lot of unknowns.

Nothing sinister has turned up in clinical trials so far, but there are still unknowns.

The future is full of unknowns.

We think that we know better those who are nearest to us. But time brings with it many more unknowns than knowns, and one knows others less and less well than one did. The shadow region becomes ever larger.