Perhaps she did not fully understand the impact of her words.

He was, of all people, the only one who would fully understand.

I don't fully understand what is going through her head.

Five years have passed since then and I still don't fully understand.

Now she needed him in some way he did not fully understand.

But you see, I still don't really fully understand what happened.

You may not fully understand the situation, but I do.

Those of us who were not there will never fully understand.

Only then, he said, can they fully understand their rights.

There were things between them she would never fully understand.