You walk into the grocery store with a five-item list: milk, eggs, chicken breast, bread, tomatoes. You leave with 15 items, including the chocolate cookies that were too tempting to pass up and the trail mix you definitely didn't need. What happened? Turns out the grocery store is set up specifically to lure you into buying more than you meant to. In fact, one expert on the science of the supermarket says that for the average shopper, 60 percent of what's in their basket isn't what they intended to buy.