When I bought three last-minute, cheap-seats tickets to a U2 concert at the Minnesota Vikings Stadium, I expected to be in charge of the spontaneous adventure with my 16-year-old son, Rory, and his buddy, Louie, both high school juniors. But it turned out that I was on the receiving end of the night’s teachable moments. I admit to worrying a bit about escorting two teens, one with impaired vision, through a crowd of 50,000 concertgoers, to our nosebleed seats. We were as far