When Korah and his two hundred-and-fifty followers challenged Moshe, it knocked him over: And Moses heard and fell on his face. Rashi explains it was one incident too many. This was the fourth challenge that Moshe faced: the golden calf, the complainers (mitonenim), the spies, and now Korah and band of dissenters. R. Haggai Preschel offers that it was not the quantity of trouble but the quality of the troublemakers. Until now Moses excused what was going because the previous instigators weren’t worth the worry. Korah was a different story, however. His family carried the holiest items of the tabernacle and Moses felt that a challenge from such people just too much to bear.