It is not an easy thing to say 'no' to someone. However, a time comes when one gets fed up with the growing demands of others. Every person has a limit of his/her patience. After, that point one is forced to say 'no' but many times it worsens the matters as the other person feels it very offensive and unacceptable.
So, it is not a wise thing to say 'no' when one don't have any other choice left. One should not give in before someone if his/her demands are irrational and unjust. One should be firm right from the beginning, otherwise, it deteriorates the situation and when ultimately one says 'no', it creates so many problems. So, one should not spoil other's habits by accepting his/her every wish.