When I was in business school, back in the early aughts, I did a team presentation project on the topic of the male/female wage gap. To this day, I am embarrassed at my work on this project. I was young, hard-working, and idealistic, but I was unknowingly naive to the world and think I got it all wrong.

At the time, I worked at an insurance company, and there was a huge number of women in the departments I worked with at manager and director levels. I was just starting out in my career, so I was lower in rank than almost every woman I worked with, too. That may have clouded my thinking a bit, because I lacked the perspective of someone who worked in a more exclusively male-dominated work culture. I didn’t see how women were treated at other workplaces.

To prepare for our project, which was a group presentation, I did a lot of reading on the wage gap issue. It didn’t make sense to me that it could exist. I could understand if compensation amounts averaged out with a gap between male and female average wages, but I thought there had to be a sensible reason for that. It must come down to things like the type of job taken, the number of hours worked per week, the number of overtime hours worked, employee performance, and on asking for a higher salary when applying for a job. The literature I read on the subject supported that, conditionally, but was noncommittal about whether a wage gap really existed, and about what the average male and female wage numbers actually reflected.

My main logical argument against the wage gap actually meaning that there was a male/female bias in the workplace, was that if women made less money for a particular job than men, I, as a rational employer, would predominantly hire women for that job, to save money on labor. That isn’t happening; therefore, the gender pay gap did not really exist. My project team was mostly young corporate women. They agreed with me. We didn’t even really argue about it, though I remember acting a little embarrassed about the conclusion I had come to when I presented it to them. We presented on the topic based on my conclusion, and otherwise had a successful, if uneventful, presentation to our class.

The problem is, my idea of rational hiring decisions does not reflect how the world works. People make hiring decisions—and all kinds of other decisions—for reasons that don’t make rational sense at all. At the heart of these decisions are preferences, and preferences are largely affected by bias. Bias is, essentially, a preference that can’t be adequately explained. Put another way, bias just doesn’t make sense. No sense can be made from it because it doesn’t depend on sense.

I came to this conclusion shortly after my team completed that project. I have thought a lot about it since. The thought of it pops into my head unexpectedly sometimes, like the memory of a time I sang the wrong line of a song in the high school musical, in front of everybody on closing night, and it crowds out memory of the rest of my performance, across all the performances, where I made no mistakes. It’s easy to dwell on the times you get things wrong, I suppose. At least in this case I learned something.

Now that I am older and have more experience with and exposure to the world, I notice that bias is everywhere. Bias is the sort of thought virus that nibbles away at logic and replaces it with something that feels more right or more comfortable to the thinker or decider. You do not choose to be biased; if anything, bias, soaked up from the society around them, chooses you.

Since I made that business school presentation years ago, my conclusion on the topic has completely reversed. Bias must affect hiring decisions and wages to the detriment of traditionally underserved or discriminated against groups of people, including women, because it affects everything else. Moreover, you can’t go looking for it with logic, because bias is inherently illogical.