(I wish I could remember where I found this, but it's been sitting in a tab for a while.)
All subjects worthy of study have their myths and legends, and self-defense is no different. If you don't believe me, go to any firearms forum and search for "9mm vs. .45 ACP" and see what you get. Or how about the famous "I wouldn't shoot him with a .22, because if he finds out, he's gonna be real mad and hurt you!" Really, Sparky? Go look up the assassination attempt on President Reagan sometime. People got pretty mad at John Hinkley, but none of them were up to hurting him at the time.
At any rate, we are fortunate enough to have among us those who have made the effort to scientifically study some of these myths and determine the truth of the matter. In an article on Personal Defense World, Massad Ayoob takes a look at 5 particularly common myths and disassembles them for you. Go forth and get educated.