Pragmatic fallacy

A pragmatic fallacy is a logical fallacy that occurs when, because something helped someone, it will help for everyone.

The fallacy is the bastard child of hasty generalization and anecdotal evidence; it is therefore an informal fallacy.

The fallacy is sometimes confused with an appeal to consequences; this is incorrect. An appeal to consequences uses the effects of holding a belief to argue for the truth value of a proposition, while a pragmatic fallacy uses an example where something "worked" to argue for its general efficacy.

Alternate names

 * It worked for me!

Explanation
The only way to know whether something is likely to work in all cases is to try it in a representative sample of all cases. (In medicine, usually via double blind studies.) One or two people are not representative of the human race.

A big part of the fallacy is the vagueness of the term "works" — for some people, yoga "works" to make them happy, while for others, it "works" to bring them closer to brahman. This vagueness is exploited by woomeisters worldwide. Customer satisfaction is often used as an argument for a treatment's effectiveness, when it may be nothing more than a placebo effect or their personal regression to the mean.

Examples

 * Deepak Chopra was a successful doctor, yet overworked, over-caffeinated, and a smoker. After he practiced Transcendental Meditation, he lost some of these habits. Twenty years later, he's still preaching its benefits.
 * I don't know how magnetic bracelets relieve pain, I just know that they do.