I'm a huge fan of Seth Godin. I think his "Permissions Marketing" is one of the core texts of the marketing revolution talking place on the internet, in front of our eyes.
In "the dip", Seth provides his own take on failure. He addresses an important question - how to distinguish a temporary dip from the slide procceding going over a cliff.
"Winners quit fast, quit often, and quit without guilt—until they commit to beating the right Dip for the right reasons. In fact, winners seek out the Dip. They realize that the bigger the barrier, the bigger the reward for getting past it. If you can become number one in your niche, you’ll get more than your fair share of profits, glory, and long-term security. "