" No psychic powers; I just happen to know how several of the big toy companies jack up their January and February sales. They start prior to Christmas with attractive TV ads for certain special toys. The kids, naturally, want what they see and extract Christmas promises for these items from their parents. Now here’s where the genius of the companies’ plan comes in: They undersupply the stores with the toys they’ve gotten the parents to promise. Most parents find those things sold out and are forced to substitute other toys of equal value. The toy manufacturers, of course, make a point of supplying the stores with plenty of these substitutes. Then, after Christmas, the companies start running the ads again for the other, special toys. That juices up the kids to want those toys more than ever. They go running to their parents whining, ‘You promised, you promised,’ and the adults go trudging off to the store to live up dutifully to their words. "
― Robert B. Cialdini , Influence: The Psychology of Persuasion