So Mickelson talked after his round about how he made the right play (he argued left of that pin, even in the bunker, is better than other spots of the green), but got an unlucky break.
Watching the replay on the Masters website (which, by the way, might be the singularly best sporting website I've ever seen), does anything but vanity prevent Mickelson from playing short of the green -- ala Billy Casper at the 1959 US Open at Winged Foot -- and pitching up for an easy bogey/not-that-difficult par (given his short game)? I'm staring at the screen of his tap-in for his triple, and a shot short of that green leaves him an uphill pitch to an open greenfront that runs uphill all the way to the hole -- the kind of stuff he executes in his sleep (and far easier, it seems, than his truly ballsy flop shot from behind the green on 15 on Saturday that led to a birdie.)
Those stands at the left of that green really hug that bunker. Surely Mickelson is enough of a student and historian of the game to realize hitting it into the stands is sometimes not a bargain (ala Van de Velde at the '99 Open Championship). In fact, Van de Velde is who comes to mind with this shot. When interviewed after his disaster at Carnoustie, he essentially said, "What do you want me to do -- hit 7-iron/7-iron/7-iron to win the Open?"
Sure, the 4th played hard -- but it had a 2:1 ratio of pars/birdies to bogeys/others on Sunday. I guess he's still not one to play the odds and play it safely.