You have a unique id. This is your user name. It is generally some combination of your initials and names. Usually it is first initial and your last name. Some servers are limited to 8 characters total.
People tend to forget long complicated ones.
You could substitute the numerical IP address, but that would be harder to remember. Also some people have more than one e-mail address and this adds to the confusion. It's just another layer to the complexity of communication that makes life interesting. Get used to skipping the headers and reading the messages. That's to say that when you log in, your address changes ever so slightly each time.