Personally have no issues with saying No to people or to myself, I learnt that in life that it important sometimes to say no. But also my personality also as a big role in that, am not intimidated or offended by being told no by other people. I have been told enough No's and some Yes, thus its not hard for me to tell people No, when no is the most appropriate answer.
So to sum it up I can say, there various reasons to why people find it hard to say no. It could because of the culture. Especially African cultures, it could be the up bringing some people where raised without a No, they were given everything they demanded. For them all they know is yes!
Sometimes because of ones faith, religion sometimes can turn you into a hypocrite, you know you are not comfortable with something but you don't want to be seen as a bad guy, to you no and sin are synonymous.
Some people it hard to say no because of their personality.
Some can't say because of the recommendation and the badge they have been given, a NICE guy badge. You will here so and so, ooh he is a nice guy he is always there for people.
No matter what makes hard for you to say no, it is the best art to learn. Because Saying no is a sign of maturity, wisdom and proper self esteem.
Thank you for the article