Put two rookie  traders in front of the screen, provide them with your best high-probability  set-up, and for good measure, have each one take the opposite side of the trade.  More than likely, both will wind up losing money. However, if you take two pros  and have them trade in the opposite direction of each other, quite frequently  both traders will wind up making money - despite the seeming contradiction of  the premise. What's the difference? What is the most important factor separating  the seasoned traders from the amateurs? The answer is money management.  
Like dieting and working  out, money management is something that most traders pay lip service to, but few  practice in real life. The reason is simple: just like eating healthy and  staying fit, money management can seem like a burdensome, unpleasant activity.  It forces traders to constantly monitor their positions and to take necessary  losses, and few people like to do that. However, as Figure 1 proves, loss-taking  is crucial to long-term trading success.

  Figure 1 - This table  shows just how difficult it is to recover from a debilitating  loss.
Note that a trader would  have to earn 100% on his or her capital - a feat accomplished by less than 1% of  traders worldwide - just to break even on an account with a 50% loss. At 75%  drawdown, the trader must quadruple his or her account just to bring it back to  its original equity - truly a Herculean task! 
The Big One  
Although most traders are  familiar with the figures above, they are inevitably ignored. Trading books are  littered with stories of traders losing one, two, even five years' worth of  profits in a single trade gone terribly wrong. Typically, the runaway loss is a  result of sloppy money management, with no hard stops and lots of average downs  into the longs and average ups into the shorts. Above all, the runaway loss is  due simply to a loss of discipline. 
Most traders begin their  trading career, whether consciously or subconsciously, visualizing "The Big One"  - the one trade that will make them millions and allow them to retire young and  live carefree for the rest of their lives. In FX, this fantasy is further  reinforced by the folklore of the markets. Who can forget the time that George  Soros "broke the Bank of England" by shorting the pound and walked away with a  cool $1-billion profit in a single day? But the cold hard truth for most retail  traders is that, instead of experiencing the "Big Win", most traders fall victim  to just one "Big Loss" that can knock them out of the game forever.  
Learning Tough Lessons  
Traders can avoid this  fate by controlling their risks through stop losses. In Jack Schwager's famous  book "Market Wizards" (1989), day trader and trend follower Larry Hite offers  this practical advice: "Never risk more than 1% of total equity on any trade. By  only risking 1%, I am indifferent to any individual trade." This is a very good  approach. A trader can be wrong 20 times in a row and still have 80% of his or  her equity left. 
The reality is that very  few traders have the discipline to practice this method consistently. Not unlike  a child who learns not to touch a hot stove only after being burned once or  twice, most traders can only absorb the lessons of risk discipline through the  harsh experience of monetary loss. This is the most important reason why traders  should use only their speculative capital when first entering the forex market.  When novices ask how much money they should begin trading with, one seasoned  trader says: "Choose a number that will not materially impact your life if you  were to lose it completely. Now subdivide that number by five because your first  few attempts at trading will most likely end up in blow out." This too is very  sage advice, and it is well worth following for anyone considering trading FX.  
Money Management Styles  
Generally speaking, there  are two ways to practice successful money management. A trader can take many  frequent small stops and try to harvest profits from the few large winning  trades, or a trader can choose to go for many small squirrel-like gains and take  infrequent but large stops in the hope the many small profits will outweigh the  few large losses. The first method generates many minor instances of  psychological pain, but it produces a few major moments of ecstasy. On the other  hand, the second strategy offers many minor instances of joy, but at the expense  of experiencing a few very nasty psychological hits. With this wide-stop  approach, it is not unusual to lose a week or even a month's worth of profits in  one or two trades. (For further reading, see Introduction To Types Of Trading:  Swing Trades.) 
To a large extent, the  method you choose depends on your personality; it is part of the process of  discovery for each trader. One of the great benefits of the FX market is that it  can accommodate both styles equally, without any additional cost to the retail  trader. Since FX is a spread-based market, the cost of each transaction is the  same, regardless of the size of any given trader's position. 
For example, in EUR/USD,  most traders would encounter a 3 pip spread equal to the cost of 3/100th of 1%  of the underlying position. This cost will be uniform, in percentage terms,  whether the trader wants to deal in 100-unit lots or one million-unit lots of  the currency. For example, if the trader wanted to use 10,000-unit lots, the  spread would amount to $3, but for the same trade using only 100-unit lots, the  spread would be a mere $0.03. Contrast that with the stock market where, for  example, a commission on 100 shares or 1,000 shares of a $20 stock may be fixed  at $40, making the effective cost of transaction 2% in the case of 100 shares,  but only 0.2% in the case of 1,000 shares. This type of variability makes it  very hard for smaller traders in the equity market to scale into positions, as  commissions heavily skew costs against them. However, FX traders have the  benefit of uniform pricing and can practice any style of money management they  choose without concern about variable transaction costs. 
Four Types of Stops  
Once you are ready to  trade with a serious approach to money management and the proper amount of  capital is allocated to your account, there are four types of stops you may  consider. 
1. Equity StopThis is the  simplest of all stops. The trader risks only a predetermined amount of his or  her account on a single trade. A common metric is to risk 2% of the account on  any given trade. On a hypothetical $10,000 trading account, a trader could risk  $200, or about 200 points, on one mini lot (10,000 units) of EUR/USD, or only 20  points on a standard 100,000-unit lot. Aggressive traders may consider using 5%  equity stops, but note that this amount is generally considered to be the upper  limit of prudent money management because 10 consecutive wrong trades would draw  down the account by 50%. 
One strong criticism of  the equity stop is that it places an arbitrary exit point on a trader's  position. The trade is liquidated not as a result of a logical response to the  price action of the marketplace, but rather to satisfy the trader's internal  risk controls. 
2. Chart StopTechnical  analysis can generate thousands of possible stops, driven by the price action of  the charts or by various technical indicator signals. Technically oriented  traders like to combine these exit points with standard equity stop rules to  formulate charts stops. A classic example of a chart stop is the swing high/low  point. In Figure 2 a trader with our hypothetical $10,000 account using the  chart stop could sell one mini lot risking 150 points, or about 1.5% of the  account.