You might point to the unexpectedly aggressive play by Al Horford, or the burst of growth we've seen in Terry Rozier and Jayson Tatum. One might add the tenacity and resilience of Marcus Smart and Jaylen Brown, battling back from lesser injuries to provide meaningful boosts on both ends of the floor.
You could probably come up with at least three or four other factors, boosts from guys who will sit for several games in a row, then get their number called and answer with outstanding contributions even after riding pine for days, if not weeks. With so many key players hurt, nobody stays seated for long.
There's a fair amount of strategy involved too, though - Brad Stevens' wizardry with the Xs and Os has been as much of a factor in this unexpected run as anyone's on-court contributions have - so, watch the videos below to hear what the word on the street is regarding what is driving this Celtics team's success.