[TeMPOraL]

Personally, I learned to think of scientific ideas along two axis - precision and usefulness. To reuse your professor's example, in so far as you accept that Einstein and Newton were really talking about the same concept of "mass", general relativity is much more precise than newtonian mechanics - but newtonian mechanics is much more useful than relativity, is the sense that it's precise enough for 99.9% of applications (including sending spaceships around the Solar System) while also being significantly easier to use.