I agree in general with the sentiments in this thread. However, it is also useful to know what the realistic range of outcomes includes. Stephen Bigalow wrote in one of his books that a full-time trader will average about 10% per month.
That does not mean that he makes 10% every month. Some months may be much higher than that, and some months may be losses. And as Stephen trades stocks rather than forex, I assume his experience relates to stock trading.
I am not a full-time trader, and I therefore cannot comment on Stephen's numbers. However, as a sense of what is happening out there in the world, I have found that quite useful.