We define it and give it meaning.
One could argue that the current WWE environment actually has led to the death of truth, and I think people in this thread have occasionally done just that, but I think the discussions we have here all the time about specific matches and wrestlers say otherwise.
I don't deny that there are things that can be gleaned from watching footage. You can see stuff like a wrestler's physique, what moves they do, their execution, etc. The thing is that these seem more useful for someone scouting out talents than they are for ranking someone's overall ring prowess. What I disagree with is the idea that you can watch enough and somehow bridge the gap from "Stan Hansen seems great at working brawls" to "Stan Hansen is the 3rd best wrestler of all-time" or "Terry Funk is better than Stan Hansen." The former statement involves deducing that someone could succeed in filling a particular role based on what you've seen. The latter statements involve trying to figure out who's better among guys regarded as world-class without really having much of an understanding of what it's like to actually work with any of the guys being discussed. What does better even mean? It's seems kind of ridiculous that we've had so many discussions about who is a better performer while no one agrees about whether it means they had a better prime, had more great matches, or were more versatile, etc.