Comment by glenk

It makes a bit more sense(to me) if you adjust how you are looking at it. When you are choosing 1 door out of 3, your chance of being WRONG is 2/3. No matter what happens with the 2 other doors, your chance of being wrong with your original choice is still 2/3. By switching to the second set, you've doubled your chances to win. You can see this in action and try it out yourself with this code here: https://github.com/ardalis/MontyHallMvc