That said, I think "not knowing my customer" is still a sound lesson. If you know your customer, you'll know whether there is or isn't a market.
Re post-mortems, should keep you going:
http://www.chubbybrain.com/blog/startup-failure-post-mortem/
http://www.businessinsider.com/the-25-best-startup-fail-stor...
http://www.chubbybrain.com/blog/top-reasons-startups-fail-an...
http://www.chubbybrain.com/blog/top-reasons-startups-fail-an...