Why it's so hard for planes to land on water

When US Airways Flight 1549 landed in the Hudson river all 150 passengers survived. Landing a plane on the water is called ditching. Ditching is more common in smaller private planes, not large planes from companies like Boeing or Airbus. But the Miracle on the Hudson isn't the only time an aircraft has been ditched. And despite that success, landing a plane on the water can be extremely dangerous.