One of the biggest obstacles for beginner traders is that they don't understand their own psychology which leads them to make specific trading decisions. For example, we are much more reluctant to take small loses than to wait for a big winning trade. We experience much bigger anxiety from losing money than the reward of winning, also we prefer to avoid risk by taking small profits and not letting them run, but on the other hand, we don't like taking small loses and allow them to grow to disaster sizes. This is something built-in everyone's mind and only proper training and practice can make it disappear. For me, it took several years to get rid of these feelings. Also, we have excitement and adrenaline rush when we trade big, and this is addictive make us trade more and bigger size until we hit a margin call or at least a sizable loss that is than difficult to handle. Also, people prefer quick prizes than much bigger long term gains. That's why 90% of people who work on the market prefer to day trade and not to invest for 1-2-5 years. These are only a few of the obstacles, there are many more and it is nothing to do with the brokers, slippage, commissions, etc. This are all some kind of costs, but they are nothing compared to our own ignorance!