KANSAS CITY, Mo. (AP) — The competition isn't the judges. Or the rest of the field. Or even the sport she's dominated for the better part of a decade. Simone Biles conquered all of them long ago.

What drives Biles is the voice in her head, the one that tells the best gymnast in the world that perfection is the only standard, even while attempting skills that no other woman on the planet (and very few men) can match.

That's why her anger was so palpable during the opening night of the U.S. women's gymnastics championships on Friday. She shorted her triple-twisting double-flip (a "triple double"...