The problem is people don't always know their own strength.

He did not know his own strength in the least.

I know your strength as no one else knows it.

Now, only in my time, have you known your full strength.

It is not just that some people don't know their own strength.

They were the ones, after all, who knew their own strengths.

We know your strength - if one may call it by that name.

The electronic media were young, too, and did not know their own strength yet.

Now here's a definite case of a boy who doesn't know his own strength!

We know our own strengths and they tend to be each other's too.