Second is whether he realized the extent of the reaction.

Most Americans don't realize the extent in which jazz is an international music.

It was only then, with distance between us, that I realized the extent of what had just happened.

We might not even know or realize the extent of their success until it's too late.

Until that moment he hadn't realized the extent of his fear.

We didn't realize the extent to which he was chicken.

That's when we realized the extent of what was to come.

I did not realize the extent to which it had set him off until one day he came into my office.

I had not before realized the extent to which this could be true.

She did not realize the extent of the new apartment's problems until they moved in.