[9][10] O'Brien trained for his Olympic and world championships on the Palouse under Idaho's track coach Mike Keller,[10][11][12][13] and Rick Sloan of Washington State in neighboring Pullman for the field events.

However, during the U.S. Olympic Trials at Tad Gormley Stadium in New Orleans in late June, O'Brien had a disaster in the eighth event, the pole vault.

[23] O'Brien's "no height" in the pole vault was also a financial embarrassment for his main corporate sponsor, and for NBC television which was heavily promoting the upcoming Olympics.

[24] The series of commercials, entitled "Dan & Dave," were meant to build interest in Reebok and the decathletes, culminating in the Olympics in Barcelona.

[25] O'Brien's unexpected failure in New Orleans received considerable attention; Reebok adjusted by running new ads featuring him cheering on Dave, who went on to win the bronze medal.

[32][33][34] After a break from competition, he won the Goodwill Games title in 1998, held east of New York City on Long Island, his eleventh consecutive win since 1992.

[35] A plantar fascia injury to his left foot in July 2000, shortly before the U.S. Olympic Trials, caused his withdrawal and he did not defend his title.

[40] Shortly following the 2010 MLB season, O'Brien began working with San Francisco Giants third baseman Pablo Sandoval, in an effort to help the struggling slugger lose weight.

[42] On June 1, 2012, O'Brien released a book which was co-written with Brad Botkin, "Clearing Hurdles: The Quest to Be The World's Greatest Athlete" (ISBN 978-1935628088).