One of the hardest things that you face is to say "no". This is true for some people and for others; its the opposite. I have sat down at meetings with some people who's very first word is "no". You propose anything or ask a question; the answer will be "NO". At first I really hated this; but at later stages started to realize that this is a better approach.
At work; especially when you work to provide others solutions. Everyone comes to you with their problems. If you start to say "yes" to all problems, then the end result is you will end up not providing anyone with a solution. So here you have to choose between priorities and stuff. Thus resulting to say a lot of "No"'s. And this is no easy job as it sounds. You don't want them to say "no" to you, when you go to them. So the trick here is you have to put it in such a way that, the "no" does not come back to you. Well.. "NO"!