I think "Smart Work" pays more than "Hard Work". One can work tirelessly day and night on something, yet make no advancement because they aren't trying to innovate or learn something new.

This goes not only for career or business but physically and mentally too. One can spend years doing 100-push ups a day and yes, you will be fit but you will eventually plateau and find diminishing returns. One can keep producing the same high quality good but when another company comes along with the same thing with some added value or at a better profit margin they will eventually do better than you.
Working hard and smart go hand in hand.

You can work like an ox or you can work like Bruce Lee.