This blew my mind at first, but after thinking it through it is better to switch. It doesn't cross peoples minds that the host KNOWS where the goat is.

It's easier to see with more doors also. Someone used an example with one million doors but his logic was flawed because you would be dead before you could open them all.

It's easier to see the ansewer if you ten doors with 9 monkeys and a car behind them. It's a little absurd to think that after you have made your 10% chance pick and then the host shows you 8 monkeys that your odds increase to 50%. The answer is more obvious even without using math if you look at two things: the host didn't randomly pick 8 doors and monkeys are more fun than goats.