7 Wonders is a classic Eurogame. It requires resource production to build upgrades which give the player points towards winning the game. In addition there are is a trading mechanism so you can utilize resources of other players. The interesting thing about 7 Wonders' resources is they act more like public goods than any other Eurogame I have played. This can result in massive underproduction of resources. Let's break down the mechanics and player incentives to see why this happens.
In 7 Wonders players each receive a hand of cards, they choose one to build, and then pass the remainder to the player next to them. This process repeats until the hand is exhausted, then a new hand of more expensive cards is dealt and the drafting continues. The game consists of 3 ages or rounds of drafting. At the end of the game points are totaled to determine the winner.
The catch with building cards is the player must be able to pay the cost listed on the card, usually some number of resources. Resources are gained in one of two ways. The first is through the cards a player has already built or as an ability of the Wonder the player is playing. This method of producing resources is permanent and usable in every build phase. So if the player can produce 1 Wood due to having that resource card, every time they build they can use that 1 Wood. But if the player has a card that costs 2 Wood, they would need access to two different sources of Wood. In later ages, cards can get very expensive requiring access to many types and large quantities of resources. This is the main incentive to drafting cards the produce resources as none of the cards give players points directly.
The second way to gain resources it to purchase them using gold from a neighbor. The twist in 7 Wonders over usual trading mechanics is this one is both non-exclusionary and non-rivalrous. This means that the player receiving the gold can't reject it and prevent the other player from using his or her resources. Further even if a player is using a resource, a neighbor can still purchase it from them. So if a player has 1 Wood that they are using to build this turn, their neighbor can also pay gold to use that Wood on that turn too.
It these interesting properties of trade that can result in a game being completely resource starved in the last age, where no new cards produce resources. In Ages I and II there is a disincentive to taking resources early because that guarantees a higher quality of cards which actually affect points at the end of the game though having more options. Plus a player following this strategy can simply buy from those that do draft the resource cards early gaining the double benefit of more resources they can access and a better quality of card choices through the resource cards being removed. And if people are at a table were everyone else is taking non-resource cards first, then it is optimal to do that too in order to maintain card quality parity and not feeding others the best cards when you are taking only resources.
When all players follow this take resources late strategy it often ends up that there are fewer resources on the field than needed for the more expensive building because the last card of an Age is discarded instead of drafted. Which leads to relatively depressing Third Ages due to everyone being resource starved. The interesting thing is this is actually optimal! It is clearly better to buy resources from others to get more scoring cards than buy resources. And any player building resources is clearly the sucker in the game as the other players use his production and snap up all the good cards. The only thing that might temper such a trading strategy is running out of gold, which is possible if the other players are not also trading due to the lower velocity of gold in such a game.
This is the only example I know of where the existence of trade and a reliance on it leads to the players getting locked out of upper tier parts of the game. It is definitely worth digging deeper into the mechanics to determine if trade having this harmful effect generalizes or what the key component of the system that makes trade harmful is.
