Studies in restaurants show that the tips left by customers who pay their
bill in cash tend to be larger when the bill is presented on a tray that
bears a credit-card logo.
事实：餐厅付现金顾客，帐单盘上面有信用卡LOGO的，会付比较多小费
Consumer psychologists hypothesize that simply seeing a credit-card logo
makes many credit-card holders willing to spend more because it reminds them
that their spending power exceeds the cash they have immediately available.
诠释/假说：看到LOGO