I rarely have to do either. Sometimes, when I want to use my directional signal, I will push the lever back and the brights will go on unintentionally. I turn them off as soon as I realize they're on.
From all the night driving I've done, I'd say the forgetfulness is usually the other way round and single-way: forgetting to dip the lights when approaching another vehicle, but often reverting to full beam too early.
So having dazzled the other driver by not dipping your ultra-intense lamps until only quarter of a mile away, you then blast his peripheral vision with a bright flash as you pass!
In fact I can't see how you could forget to put the main beams on in full darkness with no traffic approaching, because the difference between dipped and full is so great.
I deliberately do not revert to full beam until a little past the other, so I can see if another car is approaching by the glow even if around a bend, but have unfortunately sometimes dipped late. Occasionally that's when taken by surprise thanks to the other's lights being hidden beyond a local summit or blind bend, but it might be an early sign of tiredness: not good. In fact driving when too tired is now illegal, so it's a sign to find a layby for a short rest.
A hell of a lot of people also think it's illegal to drive with the fog-lamps turned off even in fully-clear air months after the last hint of the slightest mist. Errr, it's the opposite: illegal to drive with them on except in fog!
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My home gives an unexpected clue to the brightness of modern car headlamps, even on the dip beam. For a while I was puzzled by faint, momentary but definite glows on the bedroom wall opposite the window. I observed eventually that the light was from vehicles rounding a hairpin bend on a hill somewhat higher in altitude than my window, but a good two to three miles away on the straight line that light obeys.
