Your friends are liars
blog.happystuffapp.com
blog.happystuffapp.com
For the part concerning feedback, I've seen a ton of douchy founders, and want to avoid being one of them.
Disclaimer: I'm the author of the post.
PS - I'm sure the interwebs are full of things you already know ;)
looking back I reckon an awful lot of good advice and focus on our part came from our repeated (and usually unsuccessful) attempts to get early funding. Investors tended to point at what they saw as holes which forced us to think about that - either to show to ourselves they were wrong or to see that they were right and sort it out.