Skiplagging

Glad to hear that you are not brave enough.

Sometimes, if you ask nicely, the airline will drop a leg or legs of a previously booked flight so you don't have to break the contract of carriage. We had booked AVL - ATL ... Europe... ATL - AVL. Our kids were going to go with us so we could pick them up on the way to Asheville, and AVL was quite a lot cheaper than leaving from ATL. They now are not able to go, and going from ATL is preferable for us. I asked Delta to drop the AVL to ATL segments and they did, no change in fare!

As an aside, they also refunded the kids' non-refundable tickets. I don't know if they did it because of the hurricane's continued impact in Asheville, or because I'm Platinum, because there had been a few minor changes in the flights, or none of the above, but I was happy with the result.

It's pretty risky and airlines hate it, but some people like to live that way

The situation most will consider it (and also the worst time to do it) is in the middle of a round trip itinerary. Flying round trip to Rome from the US, via Paris; and someone will get the idea, "Hey, why not just leave the airport in Paris, start our vacation there, then wind up in Rome." Finding out later that the airline cancelled your return flight.

One used to do a similar trick on Eurostar, they had cheap promo one-day round trip fares Paris-London and vice versa, cheaper than a one way ticket. However, in that case, it was the ticket agent that suggested it, saved us quite a bit on three tickets.

in the UK there is a known and common way of buying train tickets that is similar to this but legal, the Man in Seat 61 is all over it

It is very hard to have sympathy for airlines.

A couple of years ago, the United gate agent in San Francisco was trying to check in people so quickly that when she swiped my ticket as she looked at my passport, the monitor didn’t turn green, instead of taking the time to re-swipe she just waved me thru. In Zurich for my connecting flight, they had cancelled my seat and I had to wait while they verified that I had actually taken the previous flight and then ended up in the very back of the plane because my good seat had been given to someone else. Hopefully, the new system of passport picture identification as you board has eliminated this problem but I now make sure the green light goes off no matter how harried the gate agent.