Annual Review of Light Switch Double-Check
The light was switched off. The room went dark. The switch was pressed again anyway.
Year in review: the light switch double-check. Period: The past year. Occurrences: Frequent. Useful information produced: approximately zero.
The Action
The light is switched off. Visual confirmation of darkness is received. The switch is pressed again.
The second press does one of two things:
A) The switch is in the off position. The second press turns it on. This is immediately noticed and the switch is turned off again. Net result: two extra seconds and confirmation that the switch was off.
B) The switch is in the off position. The second press is actually a gentle touch that registers as a press without moving the switch. The light remains off. The person experiences the tactile sensation of confirming the off position. This is the more common outcome.
The Source
The double-check originates from an event in the past, real or imagined, where a light was left on and the outcome was either an inconvenience or a mild embarrassment. The double-check is the insurance policy against that event recurring.
The double-check also originates from the gap between seeing the room go dark (visual confirmation) and trusting the visual confirmation (which apparently requires tactile confirmation).
The Signal Value
The double-check produces the following information: the switch position has been checked twice. This information is accurate. It is also information that the single check already produced.
The second check's value is psychological rather than informational. It converts "I switched it off" from a remembered action into a physically verified one.
The Year
The light was left on three times this year. None of the three were preceded by a double-check. The double-check was performed on hundreds of occasions when the light was already off.
The double-check will continue. The outcomes will be similar.