It really doesn’t, and it is easy to demonstrate by using an extreme example.
Suppose I invent a device that can detect whether there is a giant invisible dragon living in your house, and it has an accuracy of 99.999%
Now, I use it in your house and it tells me there is an invisible dragon… so what are the chances that there is a dragon in your house?
Based on your statement, it would be 99.999% likely that there is an invisible dragon in your house. However, we actually know that there is a 0% chance there is an invisible dragon, so even with the positive test result we still know there is a 0% chance a dragon is there.
Suppose I invent a device that can detect whether there is a giant invisible dragon living in your house, and it has an accuracy of 99.999%
Now, I use it in your house and it tells me there is an invisible dragon… so what are the chances that there is a dragon in your house?
Based on your statement, it would be 99.999% likely that there is an invisible dragon in your house. However, we actually know that there is a 0% chance there is an invisible dragon, so even with the positive test result we still know there is a 0% chance a dragon is there.