ignoring
Here's the simplest-possible correct explanation...
2/3 of the time, your initial pick is wrong. The host will then show you the "goat" prize (the other being the good prize). Ergo, switching will get you the good prize 2/3 of the time. 1/3 of the time you'll lose the good prize. This is obviously better than sticking with the initial choice (which is right only 1/3 of the time).How much simpler does it need to be, to be comprehensible?