Trading psychology is the most important aspect of a trader's success. This may surprise some readers, specifically those that are new to trading. However, the psychological makeup of a trader is more important than market knowledge, market analysis, and even money management. The reason psychology is so important is that even the best information can be distorted by a poor mindset.
Most new traders think the key to profiting in trading is knowing more about the market. For instance, most new traders clog their screens with every indicator they can find, read up European GDP trends, and feel that pro traders have some sort of secret knowledge. However, this inevitably does not provide the lofty results the novice trader hopes to achieve.
After realizing that excessive market information doesn't help (and may hurt) results, the next moment of truth most traders have is money management. Instead to trading 1 lot every time, or even trading the maximum lots their account will allow, these traders realize losses will happen no matter what. When you realize that everyone loses on occassion, it is easy to see why money management is necessary. This is a big step, but does not ensure success.
Now, don't get me wrong, you need to have a form of analysis and a form of money management to profit in the long term. In other words, you need an edge that when applied with proper money management leads to positive returns over the course of many trades. Great money management with no edge will only mean you lose your money more slowly. A great strategy without money management will lead to an inevitable blow up. However, without the proper mindset, it is nearly impossible to continue to get good results in the long run.
The bottom line is that a poor mindset can sabotage even the best trading strategy or money management strategy. I could write about this at great length, but we will look at one key example for now. The biggest test in trading psychology occurs during a drawdown. This occurs when a trader gets in a "slump" and has bad results for a given period of time. Usually the most devastating drawdowns eliminate a significant amount of a hard earned profit.
Keep in mind, drawdowns are completely normal. Everyone has them on occasion. However, the key is reacting properly to drawdowns. This is why trading psychology is so important. The natural reaction during a drawdown is to change your strategy. Sometimes traders will even take trades for no reason at all except for a desperate chance at a profit. Assuming you believe your methodology is sound, there is no reason to change anything during a drawdown. In fact, that is the most important time to follow the basics. Think about a baseball hitter in a slump. Sometimes they will change their stance, but usually they keep the same basic stance and swing. Instead, they focus on the fundatmentals of keeping their head still, keeping their hands back, and so on. For some reason traders tend to panic in this situation and change everything up. This leads to a larger drawdown, which usually ends when the trader reverts back to their primary strategy.