Thus we say: You never know, which is why but you never know. That is why and goes on to explain:

I don't know why, but it seems to me that bob would sound a bit strange if he said, why is it that you have to get going? in that situation. I know it originates from head shrinking, but it doesn't help me a lot to understand the etymology. Why are psychiatrists called that? Is it like my head is swollen [from anguish, misery, stress