There has been a lot of talk about how Game 4 is a "must-win," which inevitably was followed by some sniveling about how it's not really a "must-win" game, because the Flyers can, you know, still technically lose it and win the series.
But can they? Really? In the history of the NHL, a team has led 3-1 in a best-of-seven series 229 times, and has won the series 209 times. That means that teams have only come back from 1-3 down to win the series 8.7% of the time, which is not a lot (surprisingly, no one came back from a 1-3 deficit that wasn't previously an 0-3 deficit until 1987).
Don't like history? Well then let's generously assume that the Flyers would have a 50% chance of winning each of the remaining games. Their odds of winning that coin flip three times in a row would be only 12.5%.
But if the Flyers get a "must win" win in Game 4, they'll be tied 2-2. You know how often teams that are tied 2-2 win their series? 50% of the time. That's four times as much. In other words, if the Flyers win Game 4, their odds of winning this series go up 300%. And the Flyers would have two of the remaining three games at home, to boot. Who doesn't want that? It would seem that we almost must want that, mustn't we?
In more direct terms, whatever label you do or don't want to give Game 4, you can agree on this: if they don't [must] win Game 4...they'll be fucked.