this guy made a really good point about trading after 11:30, the market really seems to be out to lunch during lunch time east coast... the good action is towards the open and close of the market, mid-day is problematic. I only do very limited day trading though, I focus more on day trade style entries into short-term/swing type of trades to hike up the profit to risk ratio and hold on to them for a few days... so im not the best to give advice on daily goals, but I use different techniques to enter trades in the morning compared to the afternoon, and do my best to avoid entries mid-day... mid-day its just a garbage time of day to trade. check your own records though... you might find that a lot of your losers happen around lunch time, but maybe not, it depends on your own style. Try this... set one goal for the morning, take lunch, and set another goal for the afternoon. you should be hungry by the time lunch comes around anyway, so you can take a break without much indecision, and then you can also get well prepared for the afternoon... and again there wont be much indecision about your afternoon goal because the market will close on you anyway.
I do not believe a daily goal is useful. It indicates distrust in one's methods and work. A "I got away with it" mentality. Imagine a doctor who successully treats a patient; will he stop for the day to avoid diagnostic or treatment errors with other patients? Or any other profession - will they stop for the day after having done some work without screwing up? I trade if there are opportunities according to my methods. To me the point of trading is to make money and stopping when just that happens makes no sense. Others disagree.