From The Martial Arts Encyclopedia
Tanner's Law (for short) or "Evan Tanner Law" is an adage created on the Bullshido.net forums to address the effectiveness of using video training as a primary method to learn Martial Arts skills.
The "law", as it was formulated, reads:
YOU ARE NOT EVAN F*CKING TANNER
This is stated in such a manner to illustrate that while someone with superior athleticism and talent may be able to glean a productive knowledge of a skill set through video instruction, the vast majority of people are not similarly gifted and will not be able to reap the same benefits from such methods.