Hang around a football team long enough and you'll probably start hearing one phrase over and over again: mental toughness. Coaches, athletes, and fans alike say it's an intangible factor that separates good teams from great ones. And it turns out it's way harder to master than just about anything else in football. This week the Columbia Lions, still at the bottom of Ivy League rankings, traveled to New Hampshire to face the Dartmouth College team — their toughest opponent yet. So far this season, undefeated Dartmouth has won every game by at least three touchdowns, so the Lions will need to find that elusive mental toughness to avoid a total blowout.