Not controlling your emotion when gambling will just bring harm to your health, it will also affect the relationship to your friends and family. Worse it can lead to death. I just read a news that someone commit a suicide because he loss tons of bitcoin in leverage trading. If we know someone that have some mental problems because of gambling we should immediately take him to doctor.
We know that our emotion will affect our mind and our body. Everything we do which using emotion will give a different result, and if we use the emotion inside the gambling games, that will make a bad result for us, and we never know what the result is. If we are losing money in the gambling and our emotion become bad, then it reflects on our body, which we will be sad, angry, and another negative emotion. So we need to have a strong control for ourselves to prevent any negative emotion and we can enjoy the games without using emotion.
We feel difficult to control our emotion, but we need to learn it because we don't have a stable emotion in every day and that will be our jobs to have control for ourselves.