Staying calm in a sweaty room requires a definitive level of detachment from what lead to the situation.Feeling of detachment can itself be a measure of , when it’s a good time to speak or act
The way to deal with any difficult situation is to remain objective. The reason why some people are better than others is that some people are more able to take the emotion out of it. If a client shouts at you, it can get your back up, make you see the red mist and cause all kinds of problems. If, on the other hand, you can detach, then it becomes simply a matter of, "I'm sorry but I am unable to work for someone who shouts at people to get things done."
Sometimes you have to suppress the justice we feel, "How dare you speak to me like that..." and just keep it as their problem. Same thing with bills that aren't paid, you don't carry on working because you feel like you need their affirmation, you say, "I'm sorry but I have stopped work until my last bill is paid. If you don't pay this soon, I am likely to accept other work"