Many styles of martial arts teach and practice things that are out of the ordinary. Some claim different finger and hand formations will channel ki in the body. Some claim that the ointments they sell will help heal sprains, bruises, and other ailments. Some claim meditation will cure ills and make you a better person. There are a myriad of other boasts and claims, most of which are backed by anecdotal evidence.
Anecdotal evidence draws a conclusion from cases specifically chosen to support the argument, while ignoring cases that might tend to undermine the argument. Basically, it is accepting what someone has said is good about something and ignoring all the other people who have said something bad about it. For example, when you believing the commercial that says, "This stuff really works. Joe used it on his strained elbow and now his elbow doesn't hurt." and forgetting that for the 20 other people who used it, it had no effect. There is nothing wrong with presenting representative cases to illustrate a point as long as the cases are properly drawn from a fair sample.
The representative case serves to put a human face on what would otherwise be just a mass of cold statistics. However, it is all cases that justify the conclusion, not just the selected ones. The anecdote merely illustrates and humanizes a properly drawn conclusion. A single case, or even multiple cases, cannot replace a properly conducted study. Anecdotal evidence implies that it is illustrating a properly drawn conclusion, when in fact it is attempting to replace a proper inductive argument altogether.
Do not accept something as true just because someone says it is true. Do not believe that just because something did or did not work for one person that it will work or not work for another person. The people speaking about something may not necessarily be lying, they may have actually experienced the results they claim. Many people are affected by the placebo effect. They experience what they think they are expected to experience. That is why scientists use a test group and a control group when studying the effect of something on people. When wondering about the validity of some claim, search for independent scientific studies on the subject that have used scientific methods to draw their conclusions.