When I was made the first version I used PHP with codeigniter and used Backbone on the frontend. Which was okay for the beginning but I convinced myself that it wouldn't scale well in the long run. After reading about Node.js and it's advantages on scalability and performance over PHP, I switched the backend to use MongoDB and Node. And this happened over and over again, on many different things.
Basically, I was convinced that switching harder technologies and redesigning the UI should be done immediately and will help in the long run, because continuing with what I have now will prove difficult to change in the future. I didn't looked at it as a product but rather I looked at it technically (performance mainly).
But that was wrong, as I realized later on (in the hard way, when I ended up with big complicated mess).
I also want to blame my inner-desire to change everything; often I get bored with things looking the same way and hence I end up redesigning the entire UX just to keep myself content. (Which is a horrible thing to do when it comes to going to production; I wonder if anyone has been in the same boat as me?)