what does gladwell say a surface of examination of the canadian hockey league system would suggest

It's what's known as the relative-age effect, the results of which suggest that being born in a particular month can greatly influence an athlete's prospects for long-term success; circumstance matters just as much, if not more, than natural talent. In Gladwell's analysis it leads to what he calls an "iron law of Canadian hockey: in any elite group of hockey players - the very best of the best - 40 percent of the players will have been born between January and March, 30 percent between April and June, 20 percent between July and September, and 10 percent between October and December." It's a compelling theory as to why some hockey players become stars, and others don't. It's also not true.