People know that when an airline tells you that you have a ticket but no seat assignment, you're likely doomed for a middle seat in the bowels of the plane or will get bumped to another flight. It turns out airlines that know this, too, and have been creating artificial shortages to get you to spend more money to book a seat you may not even need.

The practice, as The Wall Street Journal's Scott McCartney explains, involves creating an "artificial shortage" of sorts by not making all the seats available when people book their tickets.  United appears to block seats, only opening them up a few hours prior to check-in. McCartney explains:

Two weeks before its July 16 departure, American Flight 34 from Los Angeles to New York showed only two middle seats in the back of the airplane available, plus 11 Preferred seats—regular coach seats toward the front without extra legroom—available for a $56.44 fee.

[...]

A week later on Tuesday, the seat map available to non-elites showed only one available middle seat, 38E, in the back of the Boeing 767-200, plus the same 11 Preferred seats at $56.44 each. But elite-level customers saw a total of 41 of 128 coach seats empty.

Think about that: one available middle seat in the back of the plane, when, in reality, there were 40 more that were actually empty. And they're not the only airlines doing it, apparently Delta, U.S. Airways and American do this too. "American Airlines blocks a large number of coach seats, both with extra legroom and without, to make them available to customers with top-level status in its frequent-flier program on every flights," McCartney writes. 

Obviously, sending travelers into anxiety isn't the ultimate goal of airlines — they're here to make money. And they achieve this by parlaying that panic and anxiety into customers buying "extra legroom" seats, which are sold for more (depending on the airline and the flight). It's a brilliant move from a business standpoint, but it's also borderline abusive. "Those seats show up on seat maps as occupied for customers without elite status, leading them to conclude seats are scarce. This prompts a portion of them to pony up," explains McCartney. 

The only reason travelers want to pony up is because they've likely seen what airlines used to do to you by giving you that "seat at check-in" option: for example, getting bumped off a flight, sitting next to the toilet, or having to check your carry-on bag and it then getting lost. We have been conditioned by airlines to be scared and wary when we're not assigned seat numbers, because, well, they love to do bad things to us

The cold-turkey remedy is to resist every urge and every fiber of your body that tells you to pull out the credit card and trust that there will be seats. The other options are, of course, pricier—keep shelling out more money until you get the frequent flier status. Or just fork over the $55 for extra leg room. You've earned it, after all.