Let's consider two traders (A & B) Trader A loses money for months or years. While he loses money he experiences a thousand AHA moments. He then integrates all this AHA moments and becomes a consistently profitable trader under all market conditions. Trader B makes lots of money consistently under particular market conditions/structure. Then when the market structure changes (like NYSE going hybrid), the trader can no longer make money (either not enough to want to continue, not as consistently, or the risk no longer justifies the return). Now you can't judge progress by P/L #s alone as the #s can lie for a long time as trader A loses consistently then masters trading and trader B wins consistently then can no longer make money. So how do you know if you're making progress or not if you can't judge by the P/L #s alone?