After finishing various levels of schooling, training and employment, and upon reaching a certain age, encountering a heretofore unknown activity provokes surprising interest. When that activity is designated with an equally novel term, the curiosity only heightens.

Consider “skiplagging.”

Would-be air travelers frustrated at the high cost of flying from Point A to Point B might ordinarily weigh traveling on less convenient dates, resort to transport by train, bus or car, or perhaps settle for visiting less expensive Point C instead. The unpleasant option of flying with stopovers may also be available, sometimes requiring an overnight stay after an unpleasant redeye flight, en route to Point B.

Envelope-pushing skiplaggers sometimes take the opposite tack.

For example, when visiting Atlanta seems prohibitively expensive, say over the recent Super Bowl weekend, purchasing a one-way ticket to Raleigh, N.C., that includes a stopover in Atlanta, might prove reasonable.

When the plane lands in Atlanta, the skiplagger grabs his carry-on bag and disembarks, forgoing the second leg of his trip.

Of course, bringing a suitcase is not possible; checked bags could be retrieved only in Raleigh. And round-trip tickets must be purchased with care; airlines will cancel the balance of a ticket once one flight is missed.

The practice is controversial for most airline tickets prohibit skiplagging in their incorporated “contracts of carriage.” Celebrated numbers geek Nate Silver wrote about “hidden city traveling” in the New York Times Magazine way back in 2011, before its current name was coined:

“Making a habit of this certainly won’t endear you to the airlines. Most of them — the major exception being free-spirited Southwest Airlines — expressly forbid it in their ticketing rules. But those rules don’t carry the force of law, and most travel lawyers say that their recourse is limited.”

In response to Silver’s piece, many readers challenged the ethics of the practice, prompting Silver to endorse it in the Times’ The Ethicist column, both because contracts of carriage are adhesion contracts and because “hidden city traveling” is a natural response to airlines employing monopoly pricing.

Limited recourse or not, airlines have tried to ground the practice of skiplagging. Their lawsuits, however, have thus far faced rough landings on both domestic and international routes.

Iberia Airlines, Spain’s flagship carrier, failed to defend its attempt to punish skiplagging passengers in the lower Spanish courts. Last November, the nation’s Supreme Court affirmed the lower court decisions, effectively legalizing skiplagging throughout the Kingdom of Spain.

United has perhaps been the most aggressive. In November 2014, together with the travel website Orbitz, it sued the Skiplagged.com website and its 22-year-old founder, Aktarer Zaman, alleging they promoted “strictly prohibited” travel. Skiplagged.com claimed to receive 1 million visits a month, prompting the Chicago federal court suit, which included allegations of unfair competition and deceptive practices.

Zaman sought to mount his defense by raising $10,000 in a GoFundMe campaign and quickly received more than $80,000 from supporters. Orbitz soon settled, but United fought on, invoking its contract of carriage, until U.S. District Judge John Robert Blakey dismissed the suit in May 2015.

Although the dismissal was on jurisdictional grounds, it appeared substantively dubious in that contracts of carriage are between airlines and passengers, not third-parties like Skiplagged. That website taunts United to this day, boasting about its victory on the homepage.

United changed tactics last year and started demanding individual passengers with high rates of skiplagging pay the fare discrepancies under threat of facing collections actions, losing their elite status or even banishment.

The latest miffed airline to take action is Lufthansa, which sought to recover the amount it claimed a Seattle-to-Oslo, Norway, trip should have cost, $2,300 on top of the $840 paid, plus interest, from the business class passenger who disembarked at the layover city, Frankfort. He then flew on to Berlin, his real destination, on a separate ticket, and rejected Lufthansa’s additional bill.

Lufthansa’s suit was thrown out in December, after the Berlin court ruled that its contract terms did not provide a comprehensible basis to recalculate the airfare, finding the airline’s method of calculating its initial price was “completely intransparent.” Lufthansa is appealing.

Even though skiplaggers break no laws and pay the fare listed for the tickets they purchase, certain airlines continue prosecuting actions against them by pointing to the contracts of carriage terms calling for each leg of a booking to be used. Navigating through the airlines’ choppy rationale of forcing consumers to utilize each segment purchased proves turbulent.

Baseball teams don’t charge fans more if they leave after seven innings, even if they come back to win in the bottom of the ninth. Bagels may be cheaper by the dozen, but if you eat only seven, the deli will not later charge the higher individual price of the rest.

When shoppers buy a gallon of milk and drink only half, the supermarket does not change the bill to two higher-cost half gallons. Costco does not revoke memberships from customers who buy a 24-pack and use only 12.

Taco Bell does not try to collect the separate $1.19 cost of the Crunchy Taco if purchasers of the $5 Chalupa Cravings Box can’t polish it off after downing the Chalupa Supreme, the Beefy 5-Layer Burrito, the cinnamon twists and the medium fountain drink.

Finally, and perhaps most apropos, Amtrak adds no surcharge if a passenger decides to hop off its California Zephyr Line in Sacramento, Calif., instead of continuing all the way to San Jose, Calif.

With little legal or common sense support for suing skiplaggers, airlines should focus on enticing paying customers, even those resourceful enough to find the most economical routes available, rather than setting collection agents or lawyers after them. Another option, of course, is to offer more nonstops.

As the computer scientist and author Paul Graham said: “You know your business model is broken when you’re suing your customers.”

To view this article as published in the Chicago Daily Law Bulletin, click here.