“做人要知足，做事要知不足，做学问要不知足。”——这是中国科学院院士、中国外科医学奠基人裘法祖的“座右铭”。其中“做事要知不足”，是因为（   ）

根据下图回答有关问题：

完成对话

A: Hey, you look unhappy. ____?

B: I need some ____. What should I get for my father's birthday?

A: How about a belt?

B: No, it's too boring.

A: What about a tie?

B: Oh no, it's so____ style.

A: Well, why don't you buy an iPhone 6？

B: Oh, my God! It's quite____.

A: Umm... A tennis racket, OK?

B: That sounds____. My father likes sports.

They have _______ habits.