http://tvtropes.org/pmwiki/pmwiki.php/Main/NotPlayingFairWithResources

This is a common form of cheating in strategy games (4X in particular). Since the player is generally much smarter than the computer, the designers compensate by giving the AI player(s) an unfair ability to gain or gather resources in order that the enemy will actually pose a challenge to the player.

This can take several forms:

AI can generate units and buildings without expending resources and/or more quickly than the player can.

Advertisement: AI gathers resources faster despite using the same technology.

AI gains resources without having to gather them.

Depending on the game, simply starting with more resources might not be cheating. The amount of resources each side starts with is determined by the designers at the start of the map, and some games never had a rule stating that all sides must begin on equal footing.

Almost never is this justified by anyone actually saying that "The enemy has a ludicrously massive amount of storage and are only gathering further to make it bigger and starve us out." line.

In some cases, the trope is justified by painting the enemy (on an ally of the enemy) as a more advanced civilization (especially aliens). Otherwise, you get Story and Gameplay Segregation. Also entirely justified at higher difficulty settings when the programmers have the simple courtesy of warning you that such settings will bend or break the rules in favor of the computer opposition.

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Compare Offscreen Villain Dark Matter. See also My Rules Are Not Your Rules, Numerical Hard, and (of course) The Computer Is a Cheating Bastard.

Examples in other video games: