Controlling greed and emotion is something that cant really be done easily unless if you do have already the experience on this market
but if not or doesnt have enough then these things will greatly affect your trading career which would really result into those bad decisions.
Losing is something that cant be avoided but somewhat can be lessen if you do already have the knowledge and experience.
Experience is one thing, character is another. I have seen veterans who still not be able to hold their emotions to a ground and I have seen noobs be able to control their emotions a lot better. Some people are a lot more cool headed than the others and they are a lot better when it comes to trading as well.
The biggest difference comes with math as well, if you are good at mathematics versus if you are horrible at it, if you are horrible at it then you will have to work really hard to understand everything talked about here, whereas if you are really good at it or already studied finance related major in college then you are going to start understanding a lot quicker as well. Sometimes it is not just experience that makes the difference however I do agree that it is one of the most major things as well, it is just not the whole of the picture and just one part of it.