It is also one of the easiest ways to bankrupt your own business.
Business Admin 101 - Approaches to combat Predatory Pricing.
http://www.fee.org/the_freeman/detail/herbert-dow-and-predat...
Predatory pricing is usually subsidized by unrelated but profitable lines of other business--which makes it sustainable (in that context).
https://en.wikipedia.org/wiki/Predatory_pricing