Trading with no stop losses. You can’t control your profits but you can control and limit your losses with a planned exit. Not having an exit plan can be very expensive when a trend starts against your position and you start hoping instead of just cutting your losses and moving on.
Your opinion can be very expensive. Trading your opinion against all other market participants can be very expensive. The market goes where it wants and when you disagree with where it is going it will cost you.
Egos are expensive things in the markets, they cause trading without stop losses. Inflated egos cause a trader’s #1 priority to be proving they are right and refusing to admit when they are wrong. It is very expensive to let ego gratification be above making money.
Trading based on predictions can cost a lot of money when they are wrong. There is more to be made by reacting to what the market is doing based on quantified signals than predicting what you think it will do later.
Stubbornness causes small losses to become big losses. It causes a trader to make the same mistake over and over because they do not assimilate feedback they keep getting the same results.
Not having an exit strategy for a winning trade can be very expensive, it is possible to ride a big winning trade into being a big loser if you do not have a predetermined plan to take profits. Trailing stops and price targets can exit and put the profits in the bank.
Trading too big of a position size for your account can be very costly because no manner how good your winning trades are you are set up to give back the profits with a string of a few big losing trades.