Externalities

While pursuing a goal, players may create new opportunities or threats for themselves or others as a side effect of their actions. This creates new goals for players, ensuring gameplay does not stall once they have achieved their primary goal.

The Game Should React to the Player

In writing, we know that audiences prefer proactive characters to reactive ones. Likewise, in game design, we want to frame players in a proactive rather than a reactive role. Practically, this means they

Designing Auctions Players Can Afford to Lose

Auction mechanics risk creating degenerate gameplay when the item bid on is so valuable that players are forced to bid it up. Generally, you want situations where players are comfortable losing an auction.