I think it is only possible to say whether one's work is great in a while after it has been done. It's a good idea to take up something that you really like and

I think it is only possible to say whether one's work is great in a while after it has been done. It's a good idea to take up something that you really like and dive into it because the fact that you like the subject raises the odds of your success. It is quite useless to look for an area where the average chances are high unless you are interested in the subject matter. In terms of the Mark's hypothesis that "our greatest life’s works will be inspired from both within and desired externally" I would definitely emphasize the "inspired from within" part.