Recently, Floyd Landis spent a week in front of an arbitration panel that will decide whether his Tour de France title will be revoked. Though we have become accustomed to steroid charges in professional sports, this case is peculiar.

Mr. Landis is alleged to have cheated under circumstances where he was virtually certain to be caught — and he knew it.

Mr. Landis began last year’s Tour as a favorite, but he trailed badly for much of the race. By 17 of the 20 stages, he found himself in a hail-Mary situation. He had to win on that last day in the mountains, and by a wide margin, if he had any remaining hope of placing at the top. That morning, he supposedly took steroids to boost his chances.

At the end of every racing day, Tour officials collect and test urine from three athletes: the overall race leader, the winner of the day’s stage, and another randomly selected rider. We are supposed to imagine Landis taking synthetic testosterone in hopes of winning big on this crucial day. If the gamble pays off and he wins, he would get doping tests that easily detect synthetic testosterone. It seems hard to believe that anyone would take a bet such as this given the inevitability of getting caught and the steep repercussions.

Yet, sadly, I can believe he cheated.

I can believe it because I see people I care about regularly taking Floyd-like gambles. One might think that when the odds of getting caught are near certain, rational people do not cheat. But my experience in teaching philosophy courses at a university suggests that this is false.

At Indiana University, where I taught as a graduate student, we were ruthless about plagiarism — the academic analog to steroid use. Because students often submit essays with sections that have been cut and pasted from Web pages, many instructors now have a severe policy: those caught plagiarizing fail the course and get a permanent mark on their transcript for misconduct with no second chances.

In every single class I have taught or have been a teaching assistant for at least one student failed for plagiarism. What makes these cases Landisesque is that I require students to submit every assignment to turnitin.com, an online plagiarism detector. This service digitally checks student papers against every last bit of searchable text on the Internet. Students know this before submitting anything to the service — yet amazingly, they continue to take the Landis gamble every semester.

I tried to curb the scourge by stating class policy more loudly on the syllabus, by devoting an entire class session to plagiarism every semester, by refusing to accept any major assignment from students until they each scored 100% on a plagiarism quiz, which they could take as many times as needed. I tried distributing an essay about why I take plagiarism so seriously — it undermines the basic meritocratic ideals of universities. But every semester plagiarism spun onto the horizon like a constellation, impervious to my efforts.

What goes through these kids’ minds when they send plagiarized papers to plagiarism detectors? This is like Landis handing cups of his own steroid-laced urine to anti-doping officials. In light of my student-plagiarizers, what is incredible is not how a good kid could do something bad under pressure.

Landis’ story is shocking for what it tells us about us: that humans are stunningly good at undermining ourselves through self-deception, especially when placed under stress.

Students who take such a gamble are inevitably self-deluded in one of two ways. All my students can distinguish clean from plagiarized passages in other persons’ work and nobody ever has trouble acing the plagiarism quiz. But some do not seem able to grasp when their own actions constitute cheating. Such students are genuinely surprised when you place their essay next to identical paragraphs from an online source. At first they say, “I see this looks bad, but … ” It takes perseverance to convince them this is bad.

In other cases, students do cheat knowingly. When confronted with evidence, they respond with a “wow, ya got me” attitude. But these students seem bewildered that they were caught. The thirst to succeed under pressure, especially if one has been faltering, seems to block us from believing that handing a jar full of steroids to a doping official — proverbially or literally — is a losing gamble.

There is something pathetic about self-destruction, about cheating when we know we will be caught. But self-deception is something more sinister. The hemispheres of the human head are star-crossed. One blinds us to a precipice, the other pushes us off it.

Mr. Klein is a postdoctoral fellow at the University of Toronto.