Sarah Poulin lost her five-year-old son Jacob to brain cancer last year. On Monday, the country watched her compete on American Ninja Warrior in his honor. Poulin trained for months after his death in October for the chance to go on the show, which Jacob had loved since age four. "After Jacob passed away, I decided that he just loved American Ninja Warrior so much, but would never be able to get to do it, that I would do it for him," said Poulin, 32. "I decided that nothing was going to stop me."