Trading for excitement & thrill Not for profits.
Many traders consider stock market as casino and trade for thrill and fun only. As soon as one has a losing trade, he wants to quickly make back the lost money. He thinks about the other things he could have done with the money, regret taking the trade and want to recover as quickly as possible. This in turn leads to further mistakes. Be patient and wait for the next high probable opportunity. Don't rush back in. 

Trading with a high ego.
Many individuals who have remained highly successful in other business ventures have failed miserably in trading game. Because they have a fairly big ego and thought they couldn't fail. Their egos become their downfall because they can not except that they would be wrong and refuse to get out of bad trades. Once again, whoever or wherever has any one come from does not concern the markets. All the charm, powers of persuasion, number of degrees & diplomas of business management on the wall or business savvy will not budge the market when you are wrong. 

Four 4-letter words that will kill you! HOPE--WISH-- FEAR--PRAY
If you ever find yourself doing one or more of the above while in a trade then you are in big trouble! Markets has own system of moving up & down. All the hoping, wishing and praying or being fearful in the world is not going to turn a losing trade into a winning one. When you are wrong just use a simple 6-letter word to correct the situation-GET OUT! 

Trading with money you can't afford to lose.
One of the greatest obstacles to successful trading is using money that you really can't afford to lose. Examples of this would be money that is supposed to be used in any other business, money to be paid for college/school fee, trading with borrowed money etc. Ultimately what happens is that when someone knows in the back of their mind that they are risking the money they can not afford to lose, they trade out of fear and emotion versus logic and no emotion. If you are in this situation It is highly recommend that you stop trading until you earn enough to put into an account that you truly can afford to lose without causing major financial setbacks. 

No Trading Plan
If you consider yourself a trader, ask yourself these questions: Do I have a set of rules that tell me what to buy, when to buy and how much to buy, not just for the next trade, but for the next 10 trades? Before I enter a trade, do I know when I will take profits? Do I know when I will get out if I am wrong? These questions form the first part of a trading strategy. There simply cannot be any expectation of success if we can't answer these questions clearly and concisely. 

Spending profits before you make them.
Nothing is more exciting then getting into a trade that blasts off and puts you into a highly profitable situation. This can cause major problems however, because this type of trade puts you in a highly euphoric state and leads to daydreaming about the huge profits still to come. The real problem occurs as you get caught up in the daydream and expectations. This causes you to not be prepared to get out as the market reverses and wipes off all your profits because you have convinced yourself of the eventual outcome and will deny the reality of the situation. The simple remedy for this is to know where and how you will take profits once you enter the trade. 

Not Cutting Losses or letting Profits run
One of the most common mistakes made by traders is that they let their losses grow too large. Nobody likes to take a loss, but failing to take a small loss early will often result in being forced to take a large loss later. A great trader is not someone who has never had a loss. Great traders have made many losses. But what makes them great is their ability to recover quickly from a string of losses. Every trader needs to develop a method for getting out of losing trades quickly. Research and learn to apply the best methods for placing protective stoploss orders. The only way to recover from many (small) losing trades is to make sure the winning trades are much larger. After a series of losing trades, it becomes difficult to hold a winning trade because we fear that it will also turn into a loss. Let your profitable trades run. Give them room to move and give them time to move.  

Not Sticking to your plans & Changing strategies during market hours
If you find yourself changing your strategy during the day while the markets are still open, be mindful of the fact that you are likely to be subject to emotional reactions of fear and greed. With rare exception, the most prudent thing to do is to plan your trading strategy before the market opens and then strictly stick to it during trading hours. 

Not knowing how to get out of a losing trade.
It's amazing that most of the traders don't have any clear escape plan for getting out of a bad trade. Once again they hope, pray wish and rationalize their position. It must be kept in mind that market does not care what you think. It does what it does and when you are wrong you are wrong! The easiest way to keep a bad trade from going really bad is to determine before you get in, where you will get out. 

Falling in love with a stock (Just Flirt).
Many traders get fascinated by just a stock or two and look for opportunities to trade in those stocks only ignoring the other profitable trading opportunities. It is because they have simply fallen in love with a stock to trade with. Such tendencies can be suicidal as far as trading is concerned. It may cost any one dearly.