I blame the Seals and Dolphins and mating Couples
It's called porpoising. You get out-of phase with the airplane's pitching evolutions. It normally starts with a nose-wheel first landing and gets out of control from there on (in leaps and bounds)....and amongst all that there's some contributory throttle openings and closures and rapidly mating couples at work.
The crash happens when you're finally seeking closure - and at the climax you will normally be "out of bounds" with your gear off.
Some airplanes are prone to it. It's a form of PIO. That means that you will have an alibi that sounds somewhat fishy on a scale of none to ZEN (i.e. your fate is sealed even though you didn't do it on porpoise).