Myths are a bit different because they not only can be about people but also non-living things. And, myths are set in the remote past (while legends are in the recent past remember?). You (the teller or the hearer) do not necessarily have to believe the myth to be truth at all to tell it. An example is, "The house is said to be haunted by the ghost of Admiral Jones." Neither the person who says this, nor those that hear (or read it) might not believe it. But, that doesn't stop the myth from it's continuation. Nor does it stop the myth from growing or being embellished through the years as it's passed down. While I said legends, fairytales and folklore remain the same story through the years, the myth often changes with the times and tellers.
Santa Claus is considered a myth by many. And the interpretation of what he looks like and how he gets from house to house on Christmas Eve varies not only from home to home on the same street, but worldwide, country to country. This is why many myths are hard to verify if they are true or not, just like some folklore.
Myths belong to our evolution of social thoughts. Do you know, primitive people have no myths according to one anthropologist? Since belief is essential to the acceptance of a myth, primitive people simply accept them and live by them. Thus they are not a myth but "characters of fact" for them. So when is a myth not a myth? Answer: When you believe it! ;)
Many Americans feel that myths evolve for the purpose of using them as some sort of rite of passage between young children, junior high school, college and into adulthood. The period of coming of age progresses with each myth and it's details. In our often over-crowded world, they claim we crave the need for a scary adventure. And often this scary incident is a bond or secret kept within a small group and the uninitiated are pushed off. An example is a myth that the school library is haunted. No specifics are given on who haunts it and why. It's just is, according to the group. And to be accepted one has to spend the night in the library alone. Thus not only is the myth the bond, but also experiencing the myth.
Sometimes legends, myths or folklore can be spoofs or puns. An example is a story about a haunted house in which the intruder gets chased by a "floating coffin." At the end of the story, when the victim is just about to get run over by the coffin he produces a box of Smith Brothers cough drops and says, "These saved his life. Why? Because these stopped "da coffin." (coughing -get it?) These types of tales are often told around campfires, at sleepovers and backyard camp-outs.
In conclusion (I know this is pretty heavy stuff)....
"What is a legend in one time and place may be a myth in another time and place and a Märchen in yet another time and place." As science proves or disproves various theories, they also support or destroy many myths in society. And, the definition of fairytale, folklore, legend and myth is all the same = A story! Believe it or not!