Practice helps. Paying attention helps. But some day something may happen that distracts you in a way that you don't expect, or you may have a mechanical issue that strikes at just the wrong time (say, when you're just clipping in or rolling to a stop, or turning a corner while going uphill). My one and only fall in clipless pedals came after about 25,000 miles --- I had a mechanical issue as I was making a very slow turn on an uphill slope; I didn't know whether to blame the rider (me) or my mechanic (me).

Also, it's very bad luck to say you've never fallen in clipless pedals. Same as bragging about not having flats.