I had a college friend who rented a room in a converted, colonial-era tavern with an odd stairway—one step was an inch higher than the others.
Long ago, the tavern keeper and his family lived on the second floor. The tavern was on the ground floor, where, according to erroneous local legend, Daniel Shays and company hatched rebellion.
With rebellion in the air and whiskey in the glass, the innkeeper needed a burglar alarm on his stairs. He built a burglar step: twelve steps to the second floor, the ninth step—the burglar step—one inch higher than the rest. The family gradually adjusted to the 9th step anomaly. However, an intruder, governed by expectation (and whiskey), would trip on the ninth step, alerting the family.
The burglar step is an ingenious trick based on our reliance on assumptions, the expectations learned through logic and experience that streamline our daily lives.
We “know” that steps are regular.
So, there’s no need to stop, scratch your head and ponder the stairs. You chug along unconcerned as long-term, implicit memory guides you, leaving you free to think consciously about all-star wrestling, bad rock lyrics, or why scrambled eggs are better than fried.
Observe your body walking upstairs. Though it takes no conscious effort, it is still a remarkable feat. The body calculates with precision how high to lift the foot, positions it for the next step while shifting body weight to enable the other foot to lift. Notice how much clearance procedural or implicit memory allows between the bottom of the foot and the step. It’s minimal—no more clearance than is necessary.
All of this is accomplished quickly, without diverting our attention, and with only a fleeting glance. This is the efficiency of procedural memory.
Consider how much we rely on procedural memory—all the things we do without conscious thinking. Procedural or muscle memory is the implicit or subconscious memory of how to do something, such as riding a bike, opening a door or walking up stairs. Once you learn these procedures or skills, you’re done learning and you’re stair walking with a fervor—as long as the stairs have predictable regular dimensions.
Implicit memory is not prepared for irregularity. That’s why the burglar step snags the intruder.
The burglar is defeated by his assumption of regularity. Are we defeated by our assumptions?
Erase you brain. Question your assumptions until verified. Look for the burglar step lurking on the stairway.