Phobias

Why are so many people afraid of needles?
Don't look, then you get pinched, and it's all over.
I'll admit, it's a little unnerving, but I'm surprised by how many people are outright terrified, and consequently don't give blood when there are drives (like today, in the Commons).

Of course, that's not fair, and slightly hypocritical, because I've been trained into shrieking when I see a live mouse. I can handle a dead one, although a dead one is gross, just like any dead thing. But a live mouse, even in a cage in a pet store, gives me the heebie jeebies.

I also don't like small spaces, or large crowds. I generally try to avoid lines, or ordering food in lines. So I have my own unreasonable phobias. I love snakes. I can tolerate bugs, even though I don't find them especially attractive. Where do these phobias or lack-there-of come from? I have a friend who tells me "you should at least try it once and I will never make you do it again if you don't like it." Should we approach all our phobias this way?