Jennifer and I just flew back from Detroit, and, boy, are our arms tired.

Michigan is my homeland, specifically Ann Arbor, and I thought that she should have at least one encounter with a University of Michigan home game in her lifetime.

If you haven’t been to one yourself, please consider this: on game day, the corner of East Main Street and South Stadium Boulevard is the sixth-largest city in the state of Michigan.

Alumni, old fans and new fans come from all over the world to attend a Wolverines football game.

Please consider this: The capacity of Sports Authority Field at Mile High is 76,125. The average attendance for a Michigan home game is more than 112,000.

Jennifer and I woke in a hotel near the Detroit airport, and watched Irma barrel through Florida on CNN. It began a day that neither one of us will ever forget.

From the hotel to Ann Arbor in a rental car on an autumn Saturday: 30 minutes.

We walked to the stadium (from a parking space I pre-arranged from my home computer) past the high school where Iggy Pop and I would have been classmates if the Smiths hadn’t skipped town.

The stadium was opened in 1927, and there have been a number of expansions. The latest one was the addition of skyboxes on top of the skyboxes on top of the skyboxes.

The music is too loud and the playlist is abhorrent — just like it is at CU games — but by halftime we both had lost our hearing, which was a partial blessing, because the halftime musical theme was a tribute to John Williams and the upcoming “Star Wars XXXVII” fatuity.

We stayed in the stadium after the game, and watched 112,000 people leave, and leave about 112,000 pounds of litter.

I said, “Bingo.”

Jennifer said, “What?”

“My next column: Why do people litter?”

“That sounds engrossing,” the facetious German said.

There was trash under the seats everywhere you looked.

Remember Keep America Beautiful’s 1971 “crying Indian” campaign?

Their recent study about littering gives two main reasons: contextual variables and personal variables.

Contextual variables include “availability of trash cans, the accumulative impact of other litter in the area, and even weather.”

Personal variables include “age, awareness, attitudes, and feelings of personal responsibility.”

The study showed that “15 percent of littering behavior had to do with contextual demands and 85 percent had to do with personal variables.”

There were plenty of trash cans everywhere, and Michigan head coach Jim Harbaugh is featured in a big screen plea for fans to dispose of litter responsibly.

Neither mattered.

Older people are less likely to litter than younger people, the study showed. I hope they didn’t spend too much time or money figuring that one out. Have you ever seen a carload of kids toss fast food leftovers out the window?

Littering isn’t just an incidental lapse in accountability and civility.

Over nine billion tons of litter ends up in the ocean every year. Over 11 billion dollars is spent every year to clean up litter.

I am not campaigning myself. Littering is an inevitability, and I am fully resigned to it.

The explanation is this: People will be people.

(If you go to Ann Arbor, go to Zingerman’s Delicatessen. We did, after the game.)

Craig Marshall Smith is an artist, educator and Highlands Ranch resident. He can be reached at craigmarshallsmith@comcast.net.