What popular startup advice is plain wrong?

This is the only one to refer to evidence (even if not cite specifics).

> Bad advice: "It's already been done." If you think your idea brings something unique and of value to the market, it doesn't matter that's its been tried before. @Robert Pakter

There are often so many variables in a business that your "different angle" will appeal to some people - and that can be enough, especially if you don't insist on massive success. Markets usually support more than one supplier. I made the mistake of thinking a competitor was the end of my business - but I made much more after than before. (Though it was far less fun...)

[ does quora really not have perma links into the list of answers? I mouse-overed all the links, and I had to view source to get the anchor names in the end... but they didn't work. ]