The first thing I ask a founder is how often does the target customer have the problem they are looking to solve and how much money are they willing to spend to solve it. The more often the customer has your problem and the more money they are willing to spend - the easier it will be (all other things being held equal) to get customers and iterate. Sequoia calls these problems hair on fire problems. The second thing I ask is who else is trying to solve the same problem and what do you know that they don't.
This is great advice and advice I wish I taken onboard earlier. As a technical founder Ive found myself making a large set of assumptions which are usually proved to be incorrect when going to the market.
Going into the market and talking to your customers early on so you can answer those two questions will really help tell you if you have a viable idea.
