Now, the reason this condition always holds in ordinary mechanics is because you're never, in that case, concerned with a huge statistical population of particles where the disorder among them is an issue.

这个条件在力学中总是成立,这是因为在力学中,我们从来没有关注过大量粒子的统计行为，而对这些系统来说,无序是很重要的。

麻省理工公开课 - 热力学与动力学课程节选