Despite the status of brand awareness as a major advertising objective, there is actually little recent literature on the behavior of brand awareness and its dynamics. The statistical analysis of a large set of data allowed us to identify some psychological mechanisms of both spontaneous and aided awareness and the structural relationship between both of them. Our results show that in many product categories there are thresholds for spontaneous awareness. The location of the threshold, and its specific importance vary from one category to another, but the structural relationship is always identical. The characteristics of the threshold are strongly dependent (50% of the variance) on the position of the leaders which one can measure using the index of memory block.These psychological phenomena can create 6 strong barrier, giving a large advantage to the initial brand, almost known by all consumers. One can therefore contrast locked and open markets.