If I take a position and my premise of bullish or bearish proves to be wrong then I have to make a decision to hold or exit with loss.
Solution:
Start with small position size.
1) First place the correct SL (Wiggle room) which if price reaches that point my premise is likely invalid. See a trader can pick the wrong side of the market and is certain to lose or he can pick the right side and get out on a minor correction and lose. A trader can also have excellent paper profits and overstay the market and paper profits evaporate. A trader can also be right on the market and wrong on timing. Correct SL placement IMO needs to take into account the above.
2) If it reaches the invalid point exit immediately with the loss. Taking a loss is really nothing. If I do number three below.
3) Immediately look for an opportunity to reverse direction and go with the correct direction the market. Then I double up position size and go in the correct direction getting my loss back and likely make a good profit on a comparable move. Say I take a loss on 4 points in the ES. I reverse and double up and on a 2 point move I am back to break even. Another point or two and I am ahead of the game. The danger is if the market gyrates back and forth then I could get whipsawed from side to side but if I catch a fairly decent trend on the doubled up reversal then a profit is basically assured.
Of course the tactic is easier said than done. It does take some nerve. But if a trader can stop worrying about money and instead focus on the important thing-namely where is the market likely to go from this point? If I can re-focus on what is going on in the market then I have a powerful tool for success and a powerful tool for correcting a mis-judgement on market conditions that caused me to suffer a loss.
Ken's Point three ( three losers and stop for the day) plus Volpri's Point three, are very sound points to be considered when considering a traders' use of self discipline in the market.