It isn't as though Memphis doesn't know how to come from behind to win a series. They did it against the Los Angeles Clippers, though Blake Griffin's injury certainly made it easier for the Grizzlies to do so.
But the San Antonio Spurs are a different animal. One with three future Hall of Fame players and a one future Hall of Fame coach. History shows that falling behind 0-2 against the Spurs would give the Grizzlies little better than a 6 percent chance to win the series.