Author Malcolm Gladwell, in his fascinating bestseller "Outliers: The Story of Success", cites neurological research showing that "10,000 hours of practice is required to achieve the level of mastery associated with being a world-class expert." This seems to apply across many different types of experts, whether they are "writers, ice skaters, concert pianists, chess players ... Even Mozart ... couldn't hit his stride until he had his ten thousand hours in".
Reflecting on my own experience, I have become consistently profitable only after 4 years of actual trading (research alone doesn't count -- real money need to be at risk.) So while the number of hours may not be exactly 10,000, the order of magnitude is about right.
So if your trading has not been profitable, ask yourself this: "Have I traded 10,000 hours yet?"