Why Is It a Big Deal When You See Someone You Know While Driving?

I have done this myself, your driving along minding your own business, and all of a sudden you see, A friend, your Mom, Brother, Sister, casual Acquaintance, whoever.

What comes next is this uncontrollable urge to let the other person know that you see them,  then  we lose our minds trying to get that persons attention so we can wave.   I've had people drive next to me Honk and wave franticlly until I look, wave back, they smile and then seemed relieved that you saw them. It's like "Hey look! I'm out driving too!" And if you don't see that person going out of their mind trying to wave to you, then you get that awkward "Your stuck up" conversation. Do you do this, or have you ever been the stuck up, or both?