That's a choice, and that choice turns out to be very interesting and really important, because if you connect these two points together, you get a straight line that has to intercept the x-axis at some point.

在这一选择下,我们会发现一件非常有趣，而且极其重要的事,当你把这两点用直线连接起来，你会发现这条直线,将与x轴在某点相交。

麻省理工公开课 - 热力学与动力学课程节选