You can lead a pop star to a great leap forward, but you can't make her jump. We've been rooting for Simpson ever since her reality show. We even like the chinks in her armor, like her weird nose and indifference to an older, hotter sister. And unlike many of her peers, Simpson makes some great singles. But there's a big gap in her credibility that has nothing to do with plastic surgery or going blond or stretching Timbaland paper-thin: Her albums simply run out of juice. Consider her third, Bittersweet World, which is headed by the nearly miraculous "Outta My Head (Ay Ya Ya)." The song should have jump-started Simpson's stalled career. But she refuses to stay on course and craps out after "Rule Breaker," a bad-girl chant with surprisingly tricky guitar fills. The rest is mostly forgettable.