The picture to the right makes it clear that Asiana Flight 214 hit the berm just short of the runway 28L threshold. But why?
Sometimes, an aircraft lands short because of a mechanical problem. For example, British Airways Boeing 777 landed short at Heathrow in 2008 when ice crystals in the fuel caused the engine to lose power during its approach to landing.
But more commonly landing short is the result of pilot error. And I've listened to the tower tapes and didn't hear any indication of an emergency. (Admittedly, that doesn't necessarily rule out a problem in the cockpit.)
Here's an animation of Korean Airlines Flight 801 that landed short and crashed in 1997 in Guam. The cause was pilot error. The crew allowed the aircraft to get too low and then waited too long to add power and go around.