On paper, there is simply no reason for a game like The Binding of Isaac to have become as huge as it has. It makes no sense -- and this is coming from the person who believed in it the most. I knew Isaac was special, but if you asked me to bet on whether Isaac would sell over one million copies in less than a year, I would have bet against it.
You see, The Binding of Isaac was made to clash against mainstream games -- it was designed to be a niche hit at best. I had hoped it would gain some minor cult status in small circles, kind of like a midnight movie from the 1970s. From any mainstream marketing perspective, I designed Isaac to fail -- and that was my goal from the start.
When I started working on The Binding of Isaac, I was still haunted by the end of Super Meat Boy's development, and the hoops we had to jump through to get there. I wouldn't say Super Meat Boy was "selling out," but it was the closest I was going to come to it when it came to playing by the rules to make sure that we could sell the game that consumed two years of our lives (and all of our money).