The most common yet serious problems of a forex trader can be the following from my point of view:
1. Lack of proper training and expertise about forex trading
2. Trading with huge lots at one point of time
3. Neglecting the importance of various risk management techniques like stop loss, take profit, etc.
4. Ignoring the significance of demo trades
5. Spending little time in demo trades
6. Selection of wrong broker
7. Lack of proper understanding about various technical and fundamental analysis tools and techniques.