What is the Hardest Word to Say?

I heard from famous songs that the hardest word to say, is "Sorry".

Perhaps for others it's true, they may find it hard to say the word. For me, saying these two words doesn't seem to be difficult at all. It's easy to acknowledge my mistakes and sincerely ask for forgiveness to someone. It feels good if I say I'm sorry and the person would say, that's okay. What is so hard for me is saying this single word, the word that really leaves so much pain. the word where we always say when someone goes away. It breaks my heart to utter this single word specially if it meant that I won't be seeing the person for quite some time.
I hate to say this word. I just want to say hello, but not Goodbye! :( Sometimes I think it's better that to see people go or it's better not to tell people that we are leaving. I just don't want the scene...I'm really sorry if I won't say goodbye!