Interview setting:

"The business model was not viable."

Which is true, and does not cast its dissolution as primarily over personality issues, which is also probably true since if the everyone had been looking at an actual pile of cash, the vision for the company would have been kicked down the road instead of being everyone's favorite distraction from the fact that there was not a large pile of cash.

Follow up with, "I think we all, really learned a lot," to emphasize it was a group effort.

If its a long term setting, don't be afraid to provide the interviewer with the potentially false impression that you would never do another startup. There are many settings that don't want potential entrepreneurs.

Good luck.

You have been asked for more details because "different visions", without an explanation, is the kind of safe answer people give when they want to hide messy breakups.

So, in my opinion, an ideal answer would be like "I thought the product would be better marketed as a SaaS for physicians, but my partner wanted to emphasize ease of use and sell directly to patients on the App Market."

Why did you break up?

We discovered that we had very visions for the company, and very different ideas about how to achieve them.

I think what Barylen was getting at is, the truth works. If that is the reason you're not working together anymore, than that is the answer. Why would the answer be anything else?

However, we all tell ourselves (and tell our) stories to make ourselves feel better about our situation. As long as you are not lying about the reason that you've left, then your stories is the truth, your truth.

If, in fact, you were embezzling company funds, than saying "we disagreed on how to deal with corporate finances" though 'true', is clearly lying.

It's fine to be disappointed with the split, while still appreciating why it happened.

You've caught on that I was pretty disappointed with it at the time.

I appreciate the reassurance, and I feel confident in the truth of my answer.

Just let it all hang out there. What did you do wrong, what did they do wrong? Was it just not the right team for the right idea?

I'be been through the worst possible breakup, and the only way to move on is master your own interpretation of events and how to be better the next time.

Don't blame others .. even if they are fault. If they are blame yourself in not finding good co-founders.

Startups are HARD. Fail, Fail, Fail again, learn each time and one day it will be your day.