Game conditions are generally derived from the behavior of the players. Loose players make loose games and tight players make tight games, etc., etc., but it really isn't that simple. Players interact to create the game conditions, and they interact not just with each other but with the environment. Sometimes it's like that butterfly who flaps its wings in France and creates a storm in Thailand. Little things can have big effects on the game conditions.

You'll seldom see tight tables suddenly become loose or passive tables suddenly become aggressive unless there is a change in two or three players. Even replacing one tight-passive player with a maniac isn't enough to change the overall character of the table.

The main changes that you'll sometimes see occur abruptly are a loose table turning tight or an aggressive table turning passive. Those changes can occur at a table with lightning speed, seemingly without warning, and if you play a strategy geared toward a particular game condition, it's those fast, unanticipated changes that can cost you a lot of money if you don't quickly realize that the change has occurred and adjust accordingly.

The way to guard against this is to be aware of clues that suggest that a swift, dramatic change in game conditions may occur. There are some events, some external to the table, some part of the game, which should heighten your vigilance about game conditions.