Let’s hear it for Memorial Day weekend at the beach. Oh, but the litter …

Every Memorial Day weekend, it seems, the sea of red cups, beer cans and cigarette butts scattered across North Avenue Beach is a warm-weather reminder that for some, the world is their trash can. And during this, the start of road trip season, the detritus scattered along some highways and byways can be jarring.

The costs are evident: The Chicago Park District alone spends about $4.7 million cleaning up the 26 miles of lakefront as well as parks across the city, and wildlife and aquatic life pay their own price when they consume littered plastic.

In an age when recycling has become the norm and cleanup campaigns are common — including the Sweden-to-U.S. fitness craze “plogging,” which combines trash pickup and jogging — litterbugs persist. Even posting “don’t litter” signs and ticketing people — the city issues around 1,000 annually — haven’t solved the problem.

So why do people litter? Some of it is explained by the pack mentality, which means we could all be susceptible to doing it, experts say. And some of it’s just plain laziness.

“They have something, it has no value to them at that point, and to carry it around is inconvenient,” says Robert Cialdini, a psychologist who has conducted a number of studies on littering and is an emeritus professor at Arizona State University. “So they can make a decision to endure that inconvenience or they can just jettison it and be done with it.”

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