Thats a big question my friend.
and heres a list
- Underestimating the power of trends in forex
- overtrading
- over leverage
- top and bottom picking
- lack of discipline
- not having a thought out plan
- revenge trading
- listening to others too much
- reading too much rubbish
- lack of patience
- being a system wh**e
- trading too many pairs
- thinking this would be easy (although eventually proved right )
and im sure there are many others that ive forgotten and are now a part of my unconcious processes
hope this helps