Saying NO and do the RIGHT thing, or?

Don't you hate saying NO to a nice friend? Yeah...it's not the easiest thing to do...but when saying NO in that particular case is CRUCIAL, you'd hope that the turned-down friend would understand your situation and be fine about it......ahh well....hopefully that friend will truly understand that I cannot say YES even if I wanna.....coz if I did, there will be another side of people who might be cross at me...so yeah, heck! it's a difficult thing.....and I hate the fact that it's still bugging me even after 3 days!!! blerhhhh......