Speed Control
The primary underlying cause of poor landings appears to be lousy speed control. Get too slow and your choices are to land short or risk stalling onto the runway and landing hard. Either way, it's hard on the airplane. Come in too fast, and the airplane floats down the runway. You then have two choices other than going around: plunk it on flat or nosewheel first, or run off the end of the runway. Either way, your airplane will be cringing in anticipation.
Few pilots would dispute that, in general, the goal of a normal landing is to put the airplane on the ground as slowly as possible, given the conditions. It's the application of the theory that seems to give people trouble.