In one of Niederhoffer's books he points out that dojis occur far more often than chance would predict. In my judgment, dojis tend to occur at turning points in stocks, fwtw. But here is the hypothesis: dojis occur because a buyer has a mandate to buy UP TO the point at which the stock opened. In other words, if the stock is 5c below the opening price, the trader can buy the available shares up to the opening price, which results in a doji. This is a bullish formation because it is the result of a buyer trying to conceal the buying activity/not wanting to stick neck out/not bid against himself etc.