Why Don Mclean Keeps Evolving Exclusive 8648389

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

Thus we say: You never know, which is why but you never know. That is why and goes on to explain: There is a subtle but important difference between the use of that and which in a.