One of my cousins contacted me on Skype about six months ago, and we've been chatting occasionally ever since. Today was one of those days, and it brought a revelation.
Him: Hey Lida!
I do actually answer to that name, due to having had an elderly grandmother who used to confuse people's names. Here, however, after a minute of reflection I remembered that he is neither elderly nor my grandmother, and made a brilliant, though, as it turned out, erroneous deduction that he actually wanted to talk to Lida and clicked the wrong line in Skype. I decided to set him right.
Me: Hi! I am not Lida.
Him: Oops... Who ARE you?
Him: Oops... I thought you were Lida all that time.
Mind you, Lida does not share my last name, which also happens to be my Skype username. Go figure...
It must be contagious, because this cousin's wife has recently sent me a couple of emails under the mistaken assumption that I am my father.