Influence probability of lottery results

For example, if two people sign ab, if they don't publish it, the probability of drawing ab is half. If a person draws A, the probability of drawing B again is 100%.

The order doesn't affect your understanding, does it?

Here is a classic question that can help you understand the difference between the two. You entered a lucky draw. Abc has three doors, and there is a big prize behind one door. The host knows which door has a big prize behind it. If door A is selected, the owner opens door B, and the back door is empty. Do you want to change to gate c? At this time, if you still choose door A, the winning rate is one-third, and if you choose door C, the winning rate is one-half! Why? The answer is your title.