The relevance of Malcolm Gladwell's book "Outliers" to poker has been discussed at length, and I want to add my experience.
A primary theme of the book is that fortunate timing and 10,000 hours of experience in a field is often what it takes to become successful.
I often think about how I may not have ever become a profitable poker player if it weren't for lucky timing. I was lucky to be caught up in the poker boom created by hole cameras on the World Poker Tour and Chris Moneymaker; I was lucky to have friends who played in $5 buy-in home games; I was lucky to play poker in a time when frequent reload bonuses made it easy for a losing player to still turn a profit; I was lucky Neteller was still around at the time so that I could easily take advantage of those bonuses; I was lucky those good times lasted long enough for me to get the experience I needed to survive on my own.
I haven't reached 10,000 hours of poker playing time yet. I figure I've averaged about 2 hours of poker practice a day since I started playing online in spring 2004, meaning I still have seven or eight years to go before I reach that point.
But the practice I did get while clearing those bonuses in my first couple of years playing online is what gave me the time I needed to read, study, write, watch videos, listen to podcasts and think about poker enough to gain a proficiency in this great game. I'm forever thankful to have been caught up in poker during its largest expansion, which gave me the opportunity to reach my poker potential.