When the pressure is highest, people tend to revert to who they are, no matter how hard they are trying to eliminate their bad habits. James Harden is a fine young player that has a tendency to exaggerate contact. With the Thunder down three late in Game 3 of the 2012 NBA Finals, Harden exaggerated contact at a horrible time.
Harden was ostensibly called for a foul here, but really, he was called out for flopping. Thunder coach Scott Brooks had already instructed his team not to foul, and then Harden went out and did this. It pretty much removed any remote chance of the Thunder coming back to win.
Serves Harden right, too. Who tries flopping in a spot like this?