Our son is named Kenneth, but we have always called him Kenny because that was the name we liked. Now he's grown up, he can call himself whatever he likes, and if he chooses Kenneth, that's fine by me. If we had only named him Kenny, that option wouldn't be there.
I was given a very short, unshortenable name - Jane. As a teenager I hated it because all my mates could shorten their names into something cool - Caz (Carolyn), Wen (Wendy), Soo (Suzanne), Andy (Andrea) etc. All i could ever do was lengthen mine into a silly, girly Janey. Apparently my older sister chose my name. I have never forgiven her for it.