In the summer of 2007 MIT graduate Drew Houston applied for funding at YCombinator, he had an idea of a file storage and sharing application he had named Dropbox.
The following link will lead you to the application form he filled in with his answers: http://www.businessinsider.com/dropbox-y-combinator-application-from-2007-by-drew-houston-2013-9
That is my favourite part:
# Why would your project be hard for someone else to duplicate?
This idea requires executing well in several somewhat orthogonal directions, and missteps in any torpedo the entire product.
For example, there’s an academic/theoretical component: designing the protocol and app to behave consistently/recoverably when any power or ethernet cord in the chain could pop out at any time. There’s a gross Win32 integration piece (ditto for a Mac port). There’s a mostly Linux/Unix-oriented operations/sysadmin and scalability piece. Then there’s the web design and UX piece to make things simple and sexy.
Most of these hats are pretty different, and if executing in all these directions was easy, a good product/service would already exist.