Odds are if you're an upperclassman, you've had that experience where it's 12 AM, 1 AM, 2 AM, and you're really starting to stress over the incompletion of some problems that for some course, well frankly what this mechanism allows you to do if you're already 90 percent of the way there, you can call it a night and you can put it down and you could feel good nonetheless about where you got to.

对于上游的同学可能觉得无趣，因为他已经具备了这些经验，这时应该开始关注某些课程中,问题的不完整的部分，如果你已经学会了,里面90%的知识，你可以停工,或者把这门课扔到一边。

哈佛公开课 - 计算机科学课程节选