John Resig, Creator of jQuery, decided to write yet another javascript framework when there were already quite a few to choose from. Not only did he succeed, he changed web development forever.
Alex Payne, former API Developer Lead at Twitter, talks about the (somewhat insane) move to leave Twitter, and (somewhat more insane) choice to 'reinvent banking' with BankSimple.
Miguel de Icaza, founder of the GNOME project and creator of Mono talks about creating a clone of the .NET framework - all because he didn't like what else was out there at the time for Linux.