That guy Newton didn’t even know that inertial frames of reference weren’t absolute.
Let’s cut him some slack. He was arguing against a physics system that thought heavier things sank because they have more earth element in them.
Do we know that?
I mean, wasn’t that Einstein guy that said that if it’s true, we will never truly know it?
It never ceases to amaze me how difficult it is to come up with something worthwhile and original (pedants, no need to point out inspiration or standing on the shoulders of giants) without years of work. Art, science, music, whatever. Yeah, there are lucky one-offs, but even something as simple sounding as “For every action, there is an equal and opposite reaction” distills the semi-intuitive into something concrete and explainable.
or moves at constant speed
Also, it’s not just people that punch you back, things punch you back too.
He did not come up with the principle of inertia, it was already employed.