A lot of people automatically call me Liz when they first hear my name. It's unfortunate for me, because I'm not too fond of the nickname. I prefer Elizabeth, that's just who I am. While I don't really correct friends anymore, I do introduce myself as Elizabeth and will correct them gently ("So Liz..." "Elizabeth, please."). And I do make a point to call another by the name they insist they like being called: I will never assume that Oliver prefers Ollie or that Grace doesn't enjoy her nickname.
I'm not the type to really make assumptions. I don't assume everyone is healthy, but unfortunately a lot of people do. Someone once yelled at me for sitting on a train when there was clearly a disabled person in need of a seat: Himself (It was not visibly obvious he was handicap). I had put in a full day of stairs, walking and even running to catch a train and I was obviously exhausted. I'm quite aware he picked on me just because I'm young. Another time a person informed me they could see my limp was clearly fake, and that they could see I was just looking for attention. In my own defence, I didn't even know I was limping until that person informed me of my act.
I think a lot of people like to be correct. I know I do. So that's why I don't assume anything anymore. I'd rather learn and have correct vision, than be ignorant and hurt someone.