Happy workers tend to be productive workers because happiness can give them energy, enabling them to work hard, think clearly and stay engaged in whatever they're doing. On the other hand, unhappy workers can be disengaged and unproductive -- and, according to a new study from Harvard University, end up costing America $300 billion each year. Unhappy employees call in sick more often and, of course, don't work hard when they are in the office. Just the fact that disengaged employees don't bring any new ideas to the table costs employers big money.