Thaler says mental accounting. As with financial accounts, people need to close their mental books and balance their accounts. But people in different professions unconsciously balance their books at different times. Standard wage employees may balance books on a biweekly or monthly basis, which is typically when they get paid. Cab drivers, in contrast, balance their mental books every day. Since business is brisker in the rain, once drivers hit their mental income targets for the day, they go home, leaving fewer cabs when you really need them.