Should you hire people based on how optimistic they are?

Salespeople hired based on optimism alone outsold their more pessimistic counterparts by 57%:

Via The Happiness Advantage: The Seven Principles of Positive Psychology That Fuel Success and Performance at Work:

…testing revealed that the agents with more optimistic styles sold 37 percent more insurance than those with pessimistic ones, and that the most optimistic agents actually sold fully 88 percent more than the most pessimistic ones. Furthermore, agents who were more optimistic were half as likely to quit as were the pessimists.

This was the answer MetLife was looking for. They decided to hire a special force of agents picked solely on the basis of explanatory style. And it paid off. The next year, these agents outsold their more pessimistic counterparts by 21 percent; during the second year, by 57 percent.