Perhaps the culture had cultivate us not to reject or say no upon people's request, so, no matter we happy or not, we will always say YES as the standard answer.
I heard several cases from people around me, they felt guilty to say NO when people request something they really don't like to do:
Case 1: My nephew
One day, he told me that his friend A, want to borrow money from friend B. Nephew told me that friend A has a bad reputation as he like gambling. Nephew used to lend him RM200 because he didn't know friend A always lying. After that, friend A always finding excuses not to paying back the money. Mind you, my nephew still studying at a local university, and he is not so loaded.
Now, friend A wanna borrow RM1000 from friend B, saying wanna repair his car (apparently, he needs money to pay off his gambling debts). So, my nephew was helping friend B to find some excuses not to lend money to friend B. Do you think this is necesary? Why can't we just say NO directly? Do you think a person like friend A worth to be your friend?

Case 2: My Chubby-boy
Recently, Chubby-boy dad's friend's friend friend's aunt's mother-in-law's daugther's son's wife's father's sibling (a.k.a not-so-friend-one) request to balik kampung (go back to hometown) together during festive session. Mind you again, the not-so-friend-one family is doing some business which can't exposed under the sun (I hope you would understand).
Chubby-boy really don't want to ride with three them, because afraid of some unnecessary troublesome. Now you know how important is the reputation. I totally agreed with Chubby-boy. However, Chubby-boy don't know how to reject them. He keep telling me about the excuses to reject them. What I told him is, "Simply a word, NO".

I would say NO
I am shameless to say NO if some requests which I felt uncomfortable or I think you can make it by your own. I think my housemate would understand about it. For instants, KeeYit asked me to download a file for her, because it is filed in RAR format. She is unable to extract the file because she didn't have the installer. She wants me to download, then unzip then send over MSN to her. I say NO. Because I recommended her to install WinRar in solving this problem, she hesitate, then rejected my suggestion. Now you see, IF you even say NO to your own business, how could you expect people say YES to you?! Am I being so cruel to her? muhahhahaha~~!!!
I know all of these are the small matters which keep happen in our daily life. But the small matter enough to see a person's personality. I say NO it means NO, I say YES it means YES. Simple thing, but it has been complicated by our social community. What do you think? YES? NO?
