The answers focusing on hidden city ticketing are just nonsense. Airlines have much better tools for dealing with that, they can just ban you afterwards. Airli

The answers focusing on hidden city ticketing are just nonsense. Airlines have much better tools for dealing with that, they can just ban you afterwards. Airlines will resell your return ticket if you neglect contacting them after missing your first flight. If you contact them, they will not sell your return ticket. There's also a good chance that they'll switch the first flight you missed for free or at least significantly less than the cost of a new ticket.