The Most Common Way Smart, Experienced People Make Mistakes

The new year brought a new start for Singapore General Hospital’s (SGH) Accident & Emergency Department (A&E), as it moved from its old home in Block 1 to a grand, spanking new Emergency Medicine Building right next to it. Among the many new features was one particularly elegant design decision. Human factors explains why.

SGH's A&E shifted from the old Block 1, see here with the white roofs, to the towering Emergency Medicine Building right opposite from its old haunt. Source

Despite the change of address, the new A&E continues to use the very same ambulance bay as its predecessor. Experienced ambulance drivers still turn into the familiar ramp they have climbed countless times before, arriving at the resuscitation lobby without having to pause and work out where to go. When every second counts, such design choices matter. By deliberately retaining the old route, SGH spared every ambulance crew an unnecessary cognitive detour. No new approach to learn. No unfamiliar landmark to interpret. No moment of hesitation about whether a wrong turn had just been taken.

For these drivers, the journey from Singapore’s expressway arteries to the A&E is no longer something that requires conscious navigation. Like the act of driving itself, it is guided by routine and repetition, unfolding smoothly and with little deliberate thought. Practice indeed does make perfect.

Ambulances used to arrive at the old landing bay located at the far side of this image, but now need only make one additional turn to reach the new resuscitation entrance.

Many cognitive psychology concepts help explain this automaticity. In their seminal paper, Schneider and Shiffrin showed how performance begins with slow, tedious, and consciously controlled processing, but with extensive practice, actions become fast, automatic, efficient. What once required step-by-step attention becomes compressed into memory chunks and triggered almost reflexively by familiar environmental cues. This distinction was later popularized by Nobel laureate Daniel Kahneman as System 2 and System 1 thinking, the former deliberate, analytical and tiring, the latter intuitive, pattern-based, and favored even if it oversimplifies problems. A similar idea is captured in Jens Rasmussen’s Skill-Rule-Knowledge (SRK) framework, where well-practiced tasks are executed in the skill-based mode, running largely on autopilot, while novel or ambiguous situations demand a shift back to rule-based or knowledge-based control which require conscious attention.

These theories converge to highlight how automaticity is the signature of expertise. Expert actions are fast, fluent, and economical, allowing scarce mental resources to be conserved and redeployed especially when under intense pressure. Faced with a deteriorating patient, a panicking novice physician may try to focus and recall sequential protocols, evaluating each step as he takes them. An experienced clinician, in contrast, recognizes the pattern and its subtle cues almost instantly, triggering well-rehearsed diagnostic and treatment routines with little apparent effort. This efficiency creates the impression that experts always have spare capacity to achieve more, faster.

It also helps explain why seasoned drivers, more than those still under provisional plates, are often the ones caught using mobile phones at the wheel, but that's a story for another day.

Many of you are experts in your own right, and may also be victims of your own success. The very efficiency we celebrate in expertise is built on habits shaped by repetition and familiarity. When these routines are disrupted or contexts shifted, they can quietly become a source of vulnerability. You intend to take a detour to run an errand, yet find yourself sailing past the exit you were supposed to take. Your fingers type an old password that has recently been changed. You reflexively dismiss an on-screen alert, assuming it to be yet another inconsequential pop-up. A syringe of vincristine, placed within the usual setup for a spinal procedure, gets injected intrathecally by experienced doctors who knew exactly what the drug was and how it should be given.

Once a well-practiced sequence is set in motion, it tends to run to completion. Automatic behavior is stubbornly difficult to interrupt. When we are “in the flow”, actions are no longer assembled through conscious deliberation, but rather chunked together and released as a single, integrated routine. The familiar acts that precede driving off, such as fastening the seatbelt, starting the engine, shifting into gear, all unfold in a blur and executed with little awareness of each individual activity. Halting such a sequence mid-stream requires the deliberate re-engagement of conscious control, and in time-pressured, high-workload situations, that mental brake might not always be applied in time. The issue is not that experts are careless, but that their skills are so well learned that they do not yield easily to changes and interruptions.

When it comes to prompting experienced users, timing matters as much as the message itself. Rather than surfacing a computer alert on partial-dose after the clinician has already prepared the medication, it is often safer to introduce salient, informative warnings earlier, perhaps even on the patient’s medication packaging or at the point of retrieval. Better still, revamp the system so that hazardous items never appear within the flow of routine work at all. Vincristine syringes should not coexist with intrathecal setups, and concentrated potassium chloride should not sit in ward stock. When behavior is automatic, the most reliable intervention is not a reminder, but a redesign that prevents the wrong routine from being triggered in the first place.

Rather than relying on clinicians to read medication labels, an unorthodox “plunger flag” is created using a sticker to visually distinguish an uncommon multi-dose syringe from the routine single, full-dose preparation, while also introducing a small physical resistance that discourages the syringe from being fully depressed.

In the spirit of the new year and its resolutions, habit formation takes more than constant reminders. Reiterating another commentary I once wrote, updated protocols often require people to unlearn long-standing habits, many of which were forged under real operational pressures. Like returning trays or fastening seatbelts, new automatic behaviors take patience and empathy to establish, and are more readily adopted when operational friction is reduced as individuals revert to mindful, effortful control. With enough time and practice, behaviors can become so well-learned that they are executed almost unconsciously, even when they might be unnecessary or inappropriate.

So ingrained is the habit of returning used crockery that it can happen automatically, even in the face of life-threatening danger.