Shrink = Psychologist/Psychiatrist

I was reading a book earlier and came across a phrase where they refer a psychologist into a "shrink". I'm no native English speaker and I'm pretty new here in the US so I'm trying to learn the slang terms that are commonly used here. I asked my American friends about it and one said that it's because Psychologist/Psychiatrist has an ability to shrink someone's mind and another one said that it came from the word "headshrinker".

I went ahead and searched it online and I found this site www.dearshrink.com. I can't believe that there was deep reason for it and a history how they came up with the term for Psychologist/Psychiatrist.

Basically, the main reason for the term is Psychologist/Psychiatrist has the ability to shrink someone's mind into something understandable. Just like what the word shrink means, to reduce in size, Psychologist/Psychiatrist will try to eliminate some of the thoughts that has been bothering you or reduce the cause of the problem, thus, shrinking your mind. Makes sense? No?! See a shrink. :D