I reckon guys like George Smith are not common.
When people talk about the greats in sports - guys like Jordan, Kobe, Messi, Tiger etc - you often hear about their work ethic and how hard they pushed themselves (and often their teammates) in training.
A friend of mine once met Michael Hooper and he asked him if had any advice for a young player wanting to pursue a rugby career and Hooper told him that exact line - train the way you want to play.
That's true, though it's worth pointing out none of those guys play a physical contact sport like rugby.
With various changes to player safety rules, player union demands and high performance data professional rugby teams do way less contact training than they might have in the past.
Again it doesn't dispute the overall point, but the 'train like you play' applies perhaps in a different way to an ultra-physical forward like Tupou or LSL (Lukhan Salakaia-Loto) than it might to a Tom Wright or Corey Toole.