When Butler’s Shelvin Mack made what he called “the dumbest mistake of my life” against Pittsburgh, it was merely the second-silliest thing a player did in the course of six-tenths of a second.

Mack was just one of many seemingly smart players who committed a game-bending goof in the first weekend of the N.C.A.A. men’s basketball tournament. A theme has emerged, summed up in one word: Oops.

Many of the 16 teams remaining have been aided by last-minute blunders — a halfcourt shot lofted long before the buzzer, a timeout when leading in the final seconds, a misstep across the backcourt line, missed free throws, poorly timed turnovers and — in the case of Butler and Pittsburgh — back-to-back fouls, with less than two seconds left, that defied explanation.

Sure, a few games have been memorable for the anticipated artistry of game-winning shots, like the one by Morehead State’s Demonte Harper against Louisville. But those have been the exception to the rule — or rules, written and unwritten, that have largely not been followed in the final moments of tight games.