π± EMOTIONS - THIS IS THE BIG ONE!
If did not take the time to create a trading plan and backtest it, you don't really know what you are doing and emotions will have the best of you.
Fear, greed, hope, excitement, anxiousness, boredom and frustration will drive your hard earned capital away from you.
Results of these emotions are : trading too much, letting your losers run and cutting winners short, revenge trading, overleveraging etc...
I could write an entire post about each of the emotions and how they can affect you while trading, but it would make this post too lengthy. Just know that emotions are your biggest enemy when trading, for best results you should be in a stoic state when trading.