There are two primary divisions of professional day traders: those who work alone and/or those who work for a larger institution. Most day traders who trade for a living work for a large institution. These traders have an advantage because they have access to a direct line, a trading desk, large amounts of capital and leverage, expensive analytical software, and much more. These traders are typically looking for easy profits that can be made from arbitrage opportunities and news events, and these resources allow them to capitalize on these less risky day trades before individual traders can react.
Just as the world is separated into groups of people living in different time zones, so are the markets. If you start trading on the Cac 40 at 11:00 ET, you might find you’ve missed the best entry signals of the day already, minimising your potential end of day profit. So, if you want to be at the top, you may have to seriously adjust your working hours.
By aggressively trading on margin he can produce 5% daily profits on the 100k buying power he will grow their 25k cash at the rate of 20% per day. The risk of course is that he will make a mistake that will cost him everything. Unfortunately, this is the fate of 9 out of 10 traders. The cause of these career ending mistakes is a failure to manage risk.

Assess how much capital you're willing to risk on each trade. Many successful day traders risk less than 1% to 2% of their account per trade. If you have a $40,000 trading account and are willing to risk 0.5% of your capital on each trade, your maximum loss per trade is $200 (0.005 x $40,000). Set aside a surplus amount of funds you can trade with and you're prepared to lose. Remember, it may or may not happen.