FOXBOROUGH, Mass. — So here’s a dirty little secret about the Patriot Way. More often than not, Bill Belichick’s genius can be distilled to this simple coaching point: Limit your mistakes, and let your opponents beat themselves. And here at Gillette Stadium, on a crispy, sunny October afternoon, the NFL schedule makers couldn’t have picked a better matchup for New England. Here came the Detroit Lions, with their illustrious history of in-game incompetence. Here came Dan Campbell’s team, rolling into town like degenerate gamblers, banking on the league’s most forgiving defense, a new kicker tha…