Assumptions are inherently risky but ultimately you always end up having to go with your gut. That doesn't mean you shouldn't do the background research and talk to people first though! Even if you are right, you'll very likely discover that the proto idea you have now needs changing or tweaking in ways you would never have imagined had you not talked to some people in your target audience first.

I'm actually working on something right now that started like that. There are a load of large, well established incumbents operating in the market I'm about to try and pitch a tent in but none of them offer a service that does what I want. My gut told me I wasn't the only one who'd prefer my approach to the problem, so I talked to a bunch of people, refined the idea a little, did a load of research and when that all came back positive I quit my job and started building it. I'll let you know how it pans out :)

I know that as engineers we'd like to avoid talking to strangers as much as possible, but there's simply nothing better than speaking with your potential customers.

Having a competitor is a good sign, but how do you know they're profitable? How do you know they're solving the problem well enough that they're even worth imitating? How do you know they're not frustrating the hell out of their users? If you speak to potential customers, you'll know.

This is critical. As a marketer, I've seen - far too often, mind you - a severe disconnect between the perception of one's customers, and the reality.

Not saying that you need to have full personas, in which you include ALL motivations, demographics, customer journeys - the works - but it helps to have something on paper that you can refer to.

The beauty of it is you can always change them!

Well, I've been reading the competitor's press releases mainly and reviews of their product on the internet. Since I've never done this before, I just don't know how much of their frustrations I can count as a form of validation. :-)

Why are you resistant to doing the market valuation? It is cheap and beneficial. No matter hire certain you are it will validate and refine your offering. You get to learn the market size, the price point and create reasonable estimates for adoption all while collecting free feedback on features.

No matter how certain you are talk with your customers!

No resistance, just trying to get some input on how to do this stage of the process properly. In particular, I've been reading a lot of feedback on competitors' products.

I talk to people, but I need to talk to more.

If they've validated the market, then it should be easy to throw up a landing page with a pitch and a price and get people to reserve a spot in line.

Don't assume anything, get real leads and/or sales and talk to them about your planned offering and pricing.

Use data.