The bear principle is the theoretical idea that you don't need to be able to outrun an angry bear to escape; you only have to outrun the guy next to you.
Can be used as a metaphor for almost anything where the "bear" is some type of authority and you are the one trying to not get eaten. Evading police, cheating, internet piracy, drug dealing, etc.
When it comes to internet piracy, the bear principle states that while it is difficult or impossible to be completely anonymous when torrenting, IP blockers like PeerBlock will focus the attention of the "bear" on those that take no precautions at all. Anti-piracy types are not likely to go through the extra effort needed to track you when there are plenty of people who can be tracked effortlessly.