Practicing to keep calm in gambling makes a gambler more useful in dealing with disastrous situations. Gamblers who are overly affected lose money and luck is not in their favor and cannot keep calm in angry situations due to addiction.
This is not just in gambling but it happens in every other aspect of life that involves business, investment and in deals. When you are in a bad state of mind there is a tendency that it affects their ability to make good decisions this is because mentally you will be occupied by what is controlling your mindset at that moment that's why people are discouraged from making decisions or striking deals when they are in an uncomfortable position, emotionally unstable or unhappy.