Let me rephrase it.

I might rephrase it more succinctly by just saying, if you want to be a good algorithm designer, you should adopt the following mantra

So, another way to rephrase what they're saying is that if there's something every body persists so everything will stay at rest or moving at a constant velocity unless it is compelled to change its state by force, unless it is acted on by a force especially an unbalanced force, and I'll explain that in a second.