Everything does or doesn't go someplace and do something and keeps doing that until something else stops it from doing or not doing something, in which they may go do something else. However, in a case of living things, they keep going and doing until they die or it changes it's mind. It is the second part that Newton forgot to say. That is the place where he stopped. That's the only reason.
Some people stop because of murder.
That applies to the first pat of what I said. Within body were millions of small explosions, small amounts of toxic chemicals that would kill anybody.