How hard is hard enough

Not sure if it is my type A personality or the work ethic I got from my parents, I often worry about not working hard enough. Reading this article, On the Process of Becoming a Great Scientist, somehow gave me some reassurance that maybe I shouldn't worry too much about this (doesn't really help anyway). In the article, I find the part about enjoying the process of writing particularly helpful, especially given my circumstance of having to produce my dissertation soon. I think marathon is a good metaphor, there is no point of enduring the hardship if you are not going to enjoy it.