How do you prove a family legend? As with any research, you must know your subject. For instance, people often tell me they descend from George Washington. But this just isn't possible. While he apparently "slept" everywhere—if you can believe all the "George Washington slept here" signs in historical homes—the only children Washington had were his wife's from her first marriage. He never fathered children of his own, at least none that have been proven. But tracing your ancestry back to the early Colonial days could reveal many famous cousins, including a president or two. Perhaps Washington is one of them.
Another common legend is that an ancestor witnessed a historic event, such as the Wright brothers' first flight. If you know which ancestor supposedly was there, you can compare his life dates with the date of the event. Was your ancestor even alive when the Wright brothers took off from Kitty Hawk, NC?
Perhaps your family claims an ancestor lost her life aboard the Titanic, or she decided at the last minute not to board the ill-fated ship. This story is easy to verify because so much information has been published about the event, including the passenger list (see Encyclopedia Titanica). Other major events, such as battles, major disasters and epidemics, might have similar lists.
A popular, but impossible, family legend claims descent from a Cherokee princess. The problem? The Cherokee Nation didn't have royalty. Many families believe they have American Indian ancestry, but find no proof. Of course, if your family claims American Indian blood—or any other ethnic heritage—you'll want to investigate. Perhaps in your case the family story is true.
If you can, get the story down on paper. Seeing problems with family lore is often easier when it's staring back at you. Make copies of the written story. On one copy, highlight names, dates and places mentioned in the legend. On another sheet of paper, make a timeline. Include information about your ancestor as well as the celebrity in question. You might divide the paper in half and list your ancestor's life events on one side and the celebrity's on the other. Creating a timeline often brings the loopholes immediately to the forefront.