Next time you're having a bad day, head on over to Norah, Yarah, and Rosa Mukanga's joint Instagram account , and your mood will instantly improve. Collectively known as Let It Happen , the talented trio of sisters have two-stepped and shimmied their way into the social media spotlight, repeatedly going viral for their in-sync dance videos. And when I say in-sync, I mean it to the umpteenth degree. You just might think you're seeing triple while perusing their content. Twins Norah and Yarah, both 15, and Rosa, 13, grew up dancing together to the R&B and hip-hop music their parents played at home in the Netherlands. It wasn't until three years ago that they chose to brand themselves as Let It Happen, and there's a pretty sweet story behind the moniker. Prior to one of the many international dance contests they've competed in , their father was giving them a motivational speech to quell their nerves when the expression came up. "He said, 'Guys, don...