I fell into the trap that it is better to have a high % of winning trades than to cut losses and go on to the next trade. When I was trading one index, I would get a run (not unexpected) of losers (I did follow the signals) and worry that my system was failing. Then I would stop trading and look for ways to improve my system.
I finally got to call this trap, the curse of being an engineer. While practicing engineering, we were always looking for the optimal solution. This unfortunately carried over into my system development.
The real trap was I almost always would find a better system, but while looking for that better "mousetrap", I was missing a bunch of winners that the orignal system generated. So, mentally I felt better because I found the more perfect system but it hurt where it mattered in a lower account balance had I kept trading.
I never really developed the mental discipline to overcome this. What I did was scrap the one index system and go to a system that trades about 90 stocks.
This way I never really worry over a trade as I'm only putting less than 4% of my account into any single position (typically I'm in about 30 positions at a time)and the risk/stop point for each position is less than 0.3% of the account. Also, there are longs and shorts so I'm somewhat insulated from overall market moves.
When a signal comes, I take it and I don't fiddle with the system as each day I get winners to go along with the losers. It runs about 50% winners.
DS