Here's my typical thought process. I executed a long position. Thus I naturally have a bias that the market will go up.

Then,later it had shown a weakening uptrend. If I don't have detailed trading rule, I'll refuse to cut losses and find excuses to hold onto losing trades. As result, I will burn away a huge chunk of money on a losing trade.

Therefore, a detailed trading rules give me great trading accountability and reduce my bias effect. I will already have a ready plan to react to whatever market conditions, so that i can find money making opportunities and well minimize potential losses.