"The problem with that body of research is that it's difficult to interpret because obviously people with existing mental health problems use cigarettes to self-medicate."

VOA: standard.2010.06.15

Part of the problem with using operant conditioning with babies is it's difficult to get them to behave in any systematic way.

应用操作性条件作用的部分问题在于,很难使婴儿们按照系统的方式行动

耶鲁公开课 - 心理学导论课程节选

There was a conditional agreement: yes, Norway should manage this oil risk but it's politically difficult and that's the problem-- is that we're not able to do our optimal management.

他们在一定程度上同意我的观点：,是的，挪威应该设法解决石油的风险,但这在政治上很困难,其问题在于-,挪威无法做到最优的管理。

耶鲁公开课 - 金融市场课程节选