That didn't work for me. Because if you had been choosing randomly (i.e., did not know which door had the prize), my understand is that the last two doors are

That didn't work for me. Because if you had been choosing randomly (i.e., did not know which door had the prize), my understand is that the last two doors are still 50/50? It's only when the person opening the door knows where the prize is, that I should always switch?