How do we know that if they switch, Donny won’t then open Door #2 and give them the option to switch to it? For that matter, how do we know he won’t do the same with Door #3 if they stay? There’s no way to math it out due to Donny’s randomness, so they’re probably fine if they switch or stay. No matter what choice the contestant makes, the least likely outcome is that they pick the wrong door AND Donny doesn’t give them the car anyway.