In Malcolm Gladwell's Outliers he gives many examples of a phenomenon I've also witnessed in my own students over the years, and in my readings of the biographies of great writers. Gladwell puts it fairly succinctly. For someone to reach a level of competency in almost any field, sports, academia, dance, painting, blue collar jobs, an apprenticeship of roughly 10,000 hours is required. That equals roughly 10 years of hard work, committed, focused, trying and failing and trying again to learn your chosen craft.
For me the corollary to this is: If you're going to stick with something for ten years, you better be having a lot of fun doing it along the way.
Check out this video which approaches the same issue from a slightly different point of view.