In his book "Obliquity," John Kay, former director of Oxford's Biz School, says a lot of time you get to a goal only by going after it indirectly.
In business, he says, the best way to be profitable is not to try to be profitable. That is, if you focus on making money, you're likely not to pay so much attention to whether your customers are happy with the product or service and whether the working conditions are good. This might work in the short term, but it's poison in the long run.
What does that mean for writers and other creative people? To give an example in the realm of books, the writer determined to get onto the New York Times best-seller list probably will spend more time chasing trends than writing what he or she is passionate about. And the listing may go to somebody who writes a book that is unique and was written without any concern for best-seller lists.
I think it makes sense to have a goal, but then to get stuck in doing whatever you're doing and pay more attention to what's really happening than to whether it's totally compatible with the goal.
Is it bringing you unanticipated happiness or unhappiness?
Are there other opportunities cropping up that you'll miss if your eye is only on the original goal?
Is it having an effect on other people that is harmful to them or to your relationship to them?
I think obsession can lead to great achievements--but if you read the biographies of people who managed to achieve the goal with which they were obsessed, often they paid a heavy price in the other areas of their lives, such as health and relationships. Some may have considered that worth it, others may have regretted being quite so single-minded.