The cost-benefit analysis of whether to pay a bribe, he explained, "depends on how many people around me I think are also engaged in corruption.”

If most people are honest, he said, paying a bribe is a risky endeavor. There are relatively few people interested in accepting one, and many willing to report bribery to the authorities. In that scenario, the equilibrium favors honest dealing.

But “if everyone around you is paying bribes, the cost-benefit tradeoff flips,” he continued. “As more and more people engage in corruption, you’re better able to find willing partners in crime. And the benefits of staying honest decline, because everybody is cutting in front of you in line to see the doctor, or winning the contracts that you might have had a decent chance of getting.”

A new equilibrium will take hold — one that favors dishonest dealings.

That kind of corrupt equilibrium is the background to South Korea’s current scandal. Although the idiosyncrasies of the accusations against Ms. Park have grabbed global attention, the case is just the latest in a series of major corruption scandals that have erupted in the country.

In 2014, after the Sewol ferry disaster killed 302 people, including 250 high school students, an investigation revealed the ferry owner had colluded with government officials to evade safety checks. In January of this year, Prime Minister Lee Wan-koo resigned in a bribery scandal. And there have also been major scandals involving the chaebols, which are family-owned business conglomerates that hold considerable power in South Korea.

In fact, during her campaign and presidency, Ms. Park had presented herself as someone who could take on that corrupt system. Unmarried and childless, she highlighted her lack of close family as an asset to her presidency because so many previous scandals had involved steering assets to children or spouses. After the Sewol disaster, Ms. Park promised to attack the “layers of corruption” that had contributed to it.

But it now appears that Ms. Choi took advantage of the president’s isolation to gain influence over her and exploit that connection for financial and other benefits. Instead of fighting the country’s layers of corruption, the president now looks very likely to leave office disgraced and tainted by them herself.