I read this sometime during the mid-90s. I thought this was Wizard of Earthsea, but I've just reread the beginning and it's apparently not (Ged was originally Duny).
The concept is very similiar to Earthsea, a child goes to get a True Name from a wizard / wise-man. In this case the wise-man tells the child that their True Name is identical to their child-name/use-name and the boy starts shouting at him and complaining. The wise-man tells him something about being sorry, but the magic is what decided things.