How did the idea for ZocDoc evolve?

The original idea was to enable patients to go out of network, but after talking to them, we found that they really don't like doing that. Instead, we needed to let patients know which doctors are in network with their insurance, and then make it possible to book appointments online. Eighty percent of ZocDoc is what we originally planned--but if we hadn't changed the other 20 percent, we wouldn't have succeeded. There are a lot of companies that start with great ideas but miss the mark because they don't validate what they want to do.

So how do you make sure an idea will succeed?

You need to talk about it with people who will be honest with you. If the idea is bad, you want to know that as quickly as possible, so talk to people you don't know. Walk into Starbucks to start up a conversation with someone. Getting the right level of feedback is critical.

You've spent the past year trying to expand nationally. What have you learned about scaling up?

Too many companies expand in too many markets too quickly. We spent three and a half years only in New York, and half of the investors we talked to told us we were crazy, that people were going take our idea and replicate it. That's a problem if your business is easy to operate or an ideas business. But we've got all these health care IT systems, we have real technology challenges, and we have to understand how to scale everything. It probably makes sense to focus on one geography for as long as you possibly can.

Is Obamacare good or bad for health care startups?

Change is always good for entrepreneurs, because large companies can't innovate as quickly as small ones. Now, given the sensitivity of the health care industry and its regulation, there's a lot of complexity. But if you have the right expertise to innovate within health care, it can be an amazing opportunity.

From the February 2015 issue of Inc. magazine