Part of what makes Settlers of Catan such a great game is how well balanced it is. Part of that balance is the way in which the importance of various resources changes throughout the game, requiring players to adapt their strategies accordingly.
The scarce resources: Brick and Ore
The first thing to notice is that there are only three brick and ore hexes, compared to four of all the others.
Although it’s primarily the placement of the numbers that determines how abundant each resource is, fewer hexes means fewer potential settlements, so these resources tend to be less available than the others.
The early game
Building a third settlement early is important for two reasons: it boosts the amount of resources coming in, but also minimises the chance of you getting trapped with no room to expand.
For that reason the early game is often dominated by brick and wood – required both for roads and settlements. If brick is particularly scarce then the players controlling it will have a significant advantage early on.
Ore can be difficult to use in the early game unless you have a port to convert it, or can acquire wool and grain to buy development cards.
The mid game
All resources can come into play in the mid game, depending on the strategies of the players:
Players with room to expand may still be after wood and brick to keep building and going for the longest road.
Players who are fenced in but can manage to get up to 4 settlements can start focussing on cities and development cards, so ore and grain are critical.
The late game
Ore is king in the late game: cities are the easiest way to move towards winning, and they require a lot of it. The only way to win without cities is to buy development cards, which also require ore. Grain is important for the same reasons.
As space to expand becomes scarce, players who emphasised brick and wood in the early game will find it harder to spend or trade, so the trading ports for those resources can become valuable.
Winning at Catan is essentially a case of making sure you have access to the right resources at the right time. Planning ahead to make sure that you can acquire those resources through settlements, trade or ports is the key to success.