Risk management while trading is the practice of setting and maintaining tolerable loss levels given account size, trading technique, and personal thresh holds. Effective risk management is put in place on every trade, and ideally is also monitored over longer time periods such as days, weeks and months. It has been said that the biggest difference defining a professional trader from the rest is an ability to strictly follow predetermined risk guidelines. Put simply a professional trader rarely will allow himself to lose more money on any one trade than he has decided is acceptable before entering into the trade.
Risk Management Techniques
A stop loss can be the most important risk management tool for a trader. In its most basic form, a stop loss is simply a price at which the trader has decided to be the very largest loss he is willing to accept on a trade. When a stop loss is reached, the position is liquidated or covered and the loss has been accepted. A trader can accomplish this with either a stop market order or a stop limit order. The difference is that when the stop price is reached either a market order to immediately exit the position is automatically placed, or if a stop limit has been chosen a limit order is placed and the limit order will execute if the security price reaches the limit price. A stop limit order is not guaranteed to execute so it is best to be judicious when placing this stop order type. The SEC gives a good description of stop limit and stop market orders as well.
A daily loss limit is another very effective risk management tool. This sets a maximum loss level for a trader for any 1 day. When this thresh hold is reached, the trader must either liquidate all positions immediately, or else be prevented from entering into new positions.
For profitable traders, it is also a good idea to systematically remove money from their trading account. This can be a particular dollar amount every chosen period of time, or it can be a percentage of their account value, or it can even be anything above a particular thresh hold at which they decide that there is no benefit to holding a greater dollar amount in the account. The point is that if money is systematically removed, the trader will never be bankrupt in a worse case scenario (think flash crash) and hopefully a declining percentage of total net worth is subject to risk in their trading account as they make money over time.
Why Manage Risk
The point of each of these techniques is limiting personal risk during a worst case downside scenario. Every seasoned veteran knows that by nature, security price values are both unpredictable and volatile. There are opportunities to make money consistently in the market, and there is no point in losing everything in one trade, day, or even month. A professional will take the worst case scenario as a very real possibility, and plan accordingly so that they always live to make money another day. A trader never knows if any one trade will make money, but if they are confident in their system they know they will make money in the long run.
A quantified loss limit also removes emotions from decisions, and for those who plan to be professional day traders it is a necessity.