Mind you, my system has been known to fail with spectacular effects. I remember a flight from Manchester to Singapore many, many years ago, just after Christmas, when I was certain I would spend at least three-quarters of the journey sound asleep in my carefully selected window seat where no one would disturb me. I didn't count on being asked by a young married couple to switch to the seat next to the aisle so they could occupy the two inner seats of the three adjacent to the window - and then finding myself asked to move by them no fewer than eight times (yes, I counted) in the course of the flight, apologetically waking me each time, so the young lady could use the toilet.
With good fortune I may find myself next to someone reasonably civilised with a functioning bladder on the morrow. But I'm not counting on it.