Are you saying you don’t believe it? Because you explained why it works pretty well. When the host opens the door, they will always open a non-winning door, so it doesn’t affect the odds at all. There is still a 1:3 chance it’s the door you picked, and a 2:3 that it’s one of the other 2. All the host did is showed you which one it wasn’t behind, and that means the odds of that remaining door is 2:3