Because if Hillary had not failed the biggest test of her life after law school, she might not have been a Clinton.

The first time Bill Clinton proposed to Hillary Rodham was at twilight in England’s romantic Lake District in the spring of 1973. She declined.

The couple had recently graduated from Yale Law School and were at a crossroads in their two-year relationship. While the spurned Bill returned home to teach at the University of Arkansas and prepare to run for office, Hillary moved to Cambridge, Massachusetts, and rented a room near Harvard to study for the bar exam and begin work for Marian Wright Edelman at the Children’s Defense Fund.

Hillary loved Bill but could not imagine herself making a life in his home state of Arkansas. Though she had grander ambitions, she still felt pulled in two directions. And then she got a nudge in what proved to be the right direction from an unexpected source: the biggest failure of her young life — one that she kept secret from friends and the public for 30 years, and that would have historic implications as well.

The sky was the limit, or perhaps Arkansas was.

Like her Rhodes scholar boyfriend, Hillary had been a politically minded overachiever for years. The Illinois native and former Goldwater girl had become a Democrat at Wellesley College during the late 1960s and enjoyed her first taste of national fame when she delivered the commencement address at the school’s graduation — one of several student addresses featured in the June 1969 issue of Life magazine. After Yale, the sky was the limit, or perhaps Arkansas was.

As legendary Washington Post reporter Carl Bernstein chronicles in A Woman in Charge, there were plenty of reasons for Hillary to avoid Arkansas. For one, moving there would mean she’d likely have to take a teaching job like Bill or work at a local law firm — not exactly her life’s ambition. Her friends thought she was crazy to even consider it, and Bill’s mother, Virginia, who had met Hillary in New Haven, was not a big fan of hers. Bill had always dated flashier women, including a former Miss Arkansas, and Virginia was not convinced that Ms. Rodham was good enough for her son.

But after Hillary rejected his proposal in England, Bill was able to talk her into visiting Arkansas that summer … and into taking the Arkansas bar exam. Still, when Bill and Hillary parted after her brief stay in Arkansas, Bernstein writes, “their situation seemed totally unsettled.”

After sitting for the Arkansas bar exam, Hillary, along with 816 other aspiring lawyers, took the District of Columbia’s bar exam in July 1973. Passing that test was the No. 1 prerequisite to securing a decent legal job in the nation’s capital. Hillary then started her job at the Children’s Defense Fund, which she loved. Living alone in Cambridge, and without Bill, was hard, though. Hillary spent most of her salary, she later admitted, on telephone calls. “Despite the satisfaction of my work,” Clinton reflects in her autobiography, Living History, “I was lonely and missed Bill more than I could stand.”

Then, in early November, Hillary received shocking news: She had failed the D.C. bar exam. A full two-thirds of the test’s takers had passed, many of them with a far less impressive educational pedigree than hers. “For the first time in her life, she had flamed out,” writes Bernstein, “spectacularly, given the expectations of others for her.”

The future Mrs. Clinton was hardly the first person, or future leader, to fail a major examination. A Harvard Law School grad, and future first lady, named Michelle Robinson, failed her first attempt to pass the Illinois bar exam. Two future California governors, Pete Wilson and Jerry Brown, fared no better with the California bar. Winston Churchill famously failed the entrance examination to Britain’s elite Sandhurst military academy … twice.

“[M]y heart was pulling me toward Arkansas,” Clinton reflects in Living History. “When I learned that I passed in Arkansas but failed in D.C., I thought maybe my test scores were telling me something.” Northeastern University professor Daniel Urman doubts that the failure was a “deal breaker” for her move to Arkansas and that Clinton’s reading it as a sign probably stems in part from a “motivated retelling of history.” Still, it’s hard not to conjecture what turn her life — and history — might have taken had she passed the D.C. exam.

A few weeks after the bad news, Bill came to visit Hillary in Boston and the two spent time exploring the city and planning their future. He had rented a small house on 80 secluded acres outside of Fayetteville and was eager for her to join him. Which she did, taking up her own post at the University of Arkansas in 1974 after several months in D.C. working on the Senate’s impeachment inquiry staff tied to the ongoing Watergate scandal. In 1975, she finally said yes to a subsequent proposal from Bill, and the two were married in Fayetteville. Hillary would keep her exam failure hidden, however, even from close friends, for the next three decades until she mentioned it, almost in passing, in Living History. The bottom line, as she would write: “I knew I was always happier with Bill than without him.”