Days before the French president’s death, hours before the New Year, moments before a napkin was removed from his face, François Mitterrand ate two birds whole—bones, beaks, and all.

If you ever see an old photo of restaurant diners wearing napkins over their faces, you are witnessing the consumption of rare, endangered ortolan bunting birds . They are smallish songbirds, each weighing less than an ounce (see Figure 18-1). Skinny and rather plain-looking, the birds would not seem to be obvious targets for gourmands. But, in a true act of culinary barbarism, the ortolans are first force-fed, then drowned in brandy, roasted, and served whole. French custom dictates that a napkin be worn over the diner’s face, because he or she ingests the bird like a harbor seal guzzling down a herring.

The practice has been outlawed since 1999; however, in the closing hours of 1995, Mitterrand ate the ortolans and promptly died eight days later.

Had he lived longer, Mitterrand would have struggled to justify his behavior. The cruelty of drowning birds would have been reason enough to back away from the table. Additionally, his socialist sensibilities must have been vexed by such a meal, featuring a dish so shameful that the napkin was said to hide the guilty from the eyes of God.² Yet, Mitterrand ate it anyways. Twice!

Are human beings rational? If we were, then certainly we would not ride motorcycles, wear high-heeled shoes, pay more for brand-name products, flirt with bad boys and bad girls, prefer expensive over inexpensive wines, or eat endangered songbirds, among other things. Although we make some rational decisions, we make far more irrational ones.

We buy an expensive dress because “it is on sale.” We play a violent video game all day because we “need to relax.” We let children play tackle football, because “exercise is healthy.” We make irrational decisions then reframe them as rational. Psychologists call this behavior post-hoc rationalization.

Post-hoc rationalizations shape how we create products. We produce a successful or failed product then retroactively justify why it is so. Process methodologies result from post-hoc rationalizations. Agile. Scrum. Kanban. Lean. Google Design Sprints. DevOps. V-Model. Extreme Programming. Rapid Application Development. Capability Maturity Model Integration. Waterfall. Whatever. Methodologies have their merits, but they pale in comparison to reason. Rational decision-making can make nearly any project successful; a misapplied methodology can turn a golden goose into a vampire bat.

We can avoid post-hoc rationalization’s worst effects by recording our reasoning at the time we make a decision. We all rationalize; we need not compound it with forgetfulness. Documents need not be elaborate or exhaustive; a simple annotation will often suffice. As Parnas and Clements’ paper, “A Rational Design Process: How and Why to Fake It”,³ argues, the main benefit of documentation is retrospective: it allows future designers to understand not how decisions were made but why.

Post-Hoc Fallacy

With a post-hoc fallacy, we mistake correlation for causality. Watch people waiting to cross a busy street. A woman presses a button to trigger the crosswalk signal. After several seconds, the signal still says, “DONT WALK”. She presses the button again, waits a moment, and presses it a third time. The walk signal now displays, “WALK.” She may believe it takes three presses of the button to trigger the signal. Though the events seem interrelated, the first button press started a timer. Once the timer expired, the “WALK” signal was displayed. The wait is always the same whether a person presses the button one time or one hundred times. We see the same with elevator and subway door close buttons, fake office thermostat controls, and anywhere else users mistake what they observe to be what is real (see Figure 18-2).

Post-hoc fallacies may occur in marketing, economics, legal systems, and even the user experience of software. Software users frequently engage in post-hoc fallacies. They believe online forms submit faster when they repeatedly mash buttons. They believe comments are most easily read when written in ALL CAPS. They believe computers screens last longer when they use a screen saver. They believe free shipping is actually free.

Although post-hoc rationalizations and fallacies riddle user experience, we need not remedy every misconception. Some may even be beneficial. If we realized our lack of online privacy, we might stop communicating. If we recognized our lack of security, we might stop discovering. If we understood all the challenges of living and working in today’s digital world, we might stop advancing all together. A little bit of rationalization can be a good thing, allowing us to move forward and our ideas to take flight.