Your body runs on electricity. It has a rhythm. You disrupt that with an outside source, it screws up that rhythm. For lack of better words, you lose your body's retentive capabilities even if it's a split second. The sinuses go first. I'm sure I don't have to explain what's next.
Most people that get hit don't hold on long enough for the latter to happen. Which is a good thing. That's what makes 120v so dangerous. Ungrounded, you can stand and hold 120v in your hands and it just tickles. But it's disrupting your internal organs because it's overloading your natural electrical current. I'd rather get hit by 277/480 because it'll blow you off of it. The immediate damage may be more severe, but long term, it's not as bad as 120/208 which will jack up your heart.
Not a real problem for your average around the house guy. Y'all act like you've been shot when you get hit with 120v and run like cats. In my trade it's more a problem; especially with the young un's proving how tough and cool they are. "Look, I can hold this and it doesn't hurt". Morons is a good word. For all the joking around, it ain't a game. Turn it off. We don't always have that option, but it's a lot easier if you can.
On a side note and back to the humor part .... I shut down River Center Mall in San Antonio once. I was working 277 hot and my linesman's grounded against the grid, and the breaker was so old in the panel it didn't trip. So I tripped the main. You should have heard the wailing and gnashing of teeth THEN.
They're all crying because they have no power and all I'm thinking is I just blew up a good pair of pliers.