It may happen many times that we want to say 'NO' to some of the whimsical demands of our friend, boss at work, or even from some people who are in no way related, etc. but we are not able to. It happened many times with me that I was busy with a particular job even then someone asked me to help in their job, though he knew about my busy state of affairs. And I could not refuse that ultimately leading to jeopardizing my own state of work.
So, the art of refusing needs to be mastered for that matter. Its very important to make a mark about our displeasure about things we don't intent to do. Because unless we say no one is going to understand the importance of our work. We should say in a way that would not offend the person and he also understands the cause. For me it becomes impossible to refuse a person outright, a habit that does not help in the long run. Instead of putting ourselves in trouble, we can politely REFUSE, an art I need to master the most.