If you’ve read far enough in George R.R. Martin’s A Song of Ice and Fire you’ve probably met Theon Greyjoy’s people, the iron islanders. The iron isolanders feature more prominently in A Feast for Crows and A Dance With Dragons, if I remember correctly.
Theon’s father, Balon Greyjoy, is obssessed with paying the “iron price” for everything, and the iron price means using your (iron) sword and murdering some guy and taking his stuff.
The iron islanders are basically vikings, so they have to pillage everything they have. The Greyjoy house words are “We do not sow.” As in, they’re not supposed to farm. They just steal everything they need.
Balon insists that you have to pay the iron price for everything you own or have. If you’ve watched the Game of Thrones tv show you’ve seen that scene where Balon mocks Theon for not paying the iron price for that armor he has.
The thing is, the whole idea of “paying the iron price” is obviously totally unfeasible.
What about food or fishing? Why do we see fishermen among the iron islanders? What about trade? How do they survive?
Like, why would anyone else in the seven kingdoms put up with these assholes if, instead of trading, they just murdered people and took their stuff? Repeatedly? 
 Side note: Okay, everything I’m about to say aside, If you’ve read the series, “why does anyone put up with the iron islanders?” is actually a really good question. They’re generally useless and back stab and rise up in rebellion all the time. But anyway.
The answer, regarding what’s up with the iron price, is that of course it’s not feasible at all, and it’s not supposed to be.
It’s a great example of a really transparent and silly ideology that nonetheless everyone just goes along with, because hey, it greases the wheels and keeps the system working.
This is actually what makes the iron price so great. It makes no sense and stands up to not even the tiniest bit of scrutiny if you take it too literally.
But no one does, because that’s not how it works.
Instead, it’s a nuanced social code that everyone knows how to navigate in order to actually get things done:
Guy 1: “Hey, did you pay the iron price for all this stuff you obviously farmed?”
Guy 2: “Uh, sure. Yeah, technically. One of the shovels I used I took from some guy I murdered.”
Guy 1: “Cool. Well, I need some grain, so I’ll give you these coins that we’ll just assume were probably stolen at some point in the past.”
Guy 2: “Done.”
Guy 1: “Hey, I’m hungry, you got any fish? I stole these coins, you can have ’em. But I need fish.”
Guy 2: “Yeah, I got lotsa fish!”
Guy 1: “Did you pay the iron price for them?”
Guy 2: “Insofar as my fishhooks were made of iron, and I ‘stole’ them from the sea, yes, yes I totally paid the iron price.”
Guy 1: “Cool.”
See? Stuff gets done. Trade happens.