Futures players, particularly day traders and short term traders, live and die by the opening price. The threat of the opening gap is the primary motivation for many to be day traders, they are so fearful of an opening gap against them they will not carry positions overnight. It is the assumption of technical analysis that every fundamental known about a stock or commodity is reflected in the price at any given moment. Prices, other than 'noise', will not significantly change until some new perception of the future value of the stock or commodity enters the marketplace. During trading hours, other than regular government statistics at well known times, little new news enters the market.
Most markets are open seven hours or less.
Even globally traded assets have a period of no trading. These events cannot be factored into the price of the asset until the markets open. Consequently most asset classes open the next trading day at a different price than the previous close, hence the 'opening gap'. The opening is in effect a global market report of events since the close. Before we proceed with the trading implications of opening gaps just a note about open and close prices.