As it is in a lot of things, passing an tricky interview may not be the best metric of coding ability, but it is indicative of problem solving ability. It is t

As it is in a lot of things, passing an tricky interview may not be the best metric of coding ability, but it is indicative of problem solving ability. It is the same reason top companies tend to recruit from top schools. The chance that you pull a top notch programmer from a top school is higher than the chance that you pull one from a mediocre school. In the same way, the chance that the kid who passes your interview with flying colors is a good programmer is better than that of the one that completely tanks.