How unlikely are those Celtics comebacks? How often does the improbable happen in the NBA?

How unlikely are those Celtics comebacks? How often does the improbable happen in the NBA?

The ESPN app and ESPN.com include a feature that allows you to see the probability, at any point in a basketball game, that a team will win. Based on these stats, the Boston Celtics appear to be defying the odds on a regular basis. Are they really this great, or is it just a statistical…