For decades, we’ve been conditioned to expect that college tuition is one of the rare expense categories where prices seem completely immune to the market discipline of competition. But it hasn’t always been this way.

In the past 40 years, college tuition (including non-tuition fees) has increased 5.6% annually, nearly twice the 2.9% general rate of inflation. But in the almost 4 decades before that (1947-1983), tuition costs behaved like almost every other category of consumer expense and essentially matched the annual and overall changes in the general rate of inflation.

But something happened around 1983 that allowed (or caused) tuition costs to disconnect from general prices.

I asked a number of current and former college administrators their opinions about the 1983 price breakaway. Although none were aware of the date of the very clear inflection point, they did generally agree that public subsidies were declining and institutional overhead was increasing in the early 1980s, leading to a perfect storm that helped drive rapidly increased tuition.

But that doesn’t explain why parents and students willingly paid those skyrocketing costs. It does, however, explain the explosion in student debt that began about that time. In 1983, the total amount of student loans outstanding was $18.2 billion, compared to $1.8 trillion today. That 12% annual increase is twice the annual increase in tuition and four times the rate of inflation. Over that same period, the number of college students in the US increased a paltry 1.8% annually.

Before 1980, student debt was the exception, not the rule. And the small percentage of new graduates with student debt had almost miniscule balances, at least by current standards. The average student loan balance in 1980 was $3,000, compared to almost $30,000 today.

But why did this begin to change in the early 1980s?

In 1978, Congress passed the Middle Income Student Assistance Act, expanding federal student loans to all college students. The original federal Guaranteed Student Loan (GSL) program was for low income families, but beginning in 1979 all students were eligible for GSLs, regardless of income.

When those first newly eligible students graduated in 1983, the student loan explosion had begun. Loans meant that parents and students no longer had to fully or immediately confront the cost of tuition, especially since these loans were interest free until after graduation.

University administrators didn’t gather on day in the early 1980s and say, “hey; now that students can borrow unlimited cheap money, let’s raise prices forever.” But practically, that’s what happened. Easy credit meant customers became desensitized to price hikes, which meant there was no reason to stop them. This left tuition and debt feeding off each other in a self-perpetuating cycle.

That’s my theory, anyway. If you have a better explanation, I’d love to hear it.

David Moon is president of Moon Capital Management. A version of this piece originally appeared in the USA TODAY NETWORK.