Pillars of Game Development/Theme-Mechanic Balance
The balance between Theme and Mechanic can be thought of as a sliding scale on one axis. Games inevitably fall between the two extremes. Mechanical games entail more abstraction than thematic games, and games with strong theme tend towards simulation. A game that slides all the way to the theme extreme on the scale would be life itself: nothing is more realistic and immersive than reality. A game that represents the mechanical extreme might be Tic-Tac-Toe. It has absolutely no relation to reality: the objective and mode of play are unhinged from reality completely. Given these two extremes, how does a game designer construct the perfect balance for his/her game? The answer lies, in large part, in the question of what the game designer wishes to accomplish in the game design.
Another part of the answer lies in the connection between the mechanic and the theme - they are actually not so opposed as it might appear. For example, a trading game can rely on the "hard" mechanic of sell/buy and negotiation practices without losing intensity in its theme, and the same holds for sport games.