Interesting insight from Mr Wang aka Gilbert Koh:
Mr Wang Says So: My Six O'Clock Project

He's a highly successful corporate lawyer (the last I heard is that he makes more than 300k a year), a very smart man, and he said this:

"Anyway, my point is that there is little correlation between hard work and career success. People who actually get ahead in the workplace may get ahead for a wide variety of reasons, other than old-fashioned hard work."