This is Jack Dorsey, the inventor of Twitter and co-founder of Square. The whole interview is worth watching. The guy asking the questions is Kevin Rose, co-founder of Digg and now a VC with Google Ventures. I particularly like this quote from Jack about 18 minutes in:
The hardest thing about all of this is to get started. And I think the most important thing that I’ve learned is that you have to – as soon as you have it – get it out of your head, get it on paper. And then to take this one step further, just show someone. Just show someone what it looks like on paper. Even code a little bit and show someone the interaction.