After validating an idea for a physical product with users, how do you know it will also scale and move through the innovators and early adopters?

The best way to answer this question is to break the three concepts you've raised into separate pieces.

VALIDATION

You say you've validated an idea, but I'd like to know how. Did you run a kickstarter? Do you have a landing page up? What is the sample size? What metrics did you track? Do you already have people willing to pay? What other evidence have you collected to prove the market opportunity is real?

Reading between the lines, my instinct is that you haven't yet validated the idea and are early in the process. Validation should be your absolutely top priority. The other parts come later once you know the market exists. There is lots of material available to walk you through the validation process.

SCALING

You are right in the second part of your question. As a founder, you have to find ways to make your company scale. And note: it's not the product that scales, but the business model and operations behind it. Products don't scale themselves; that's the "build it and they will come" mentality. With physical products it's even harder than pure tech because you have the additional complexity of solving all the supply chain issues of production and delivery. It is possible to scale product companies, but the products definitely don't scale themselves.

So (1) a "product" won't scale, a business model does; and (2) you won't be able to know in advance because it's your responsibility to design a scalable model that will help you deliver the physical product in line with demand, on time, at quality, and at a profit.

CROSSING THE CHASM

Your reference to innovators and early adopters refers to the technology adoption life cycle covered by the book "Crossing the Chasm". There is an important note here: the "chasm" is not between early adopters and innovators, it's between those two groups and the mainstream (ie, the "early majority" or "pragmatists"). The reasons early adopters buy a product is different to the mainstream. Finding a product that appeals to a small group, but does not yet appeal to the mainstream's higher demands for quality, support, less behavioral change, etc is where companies get stuck.

It comes back to validation again. Who did you validate with? Just a group of 15 hyper adventurous tech-friendly boffins with a special interest in your area ... or are you solving a problem millions of people have and you can prove it because you've found 10,000+ of them willing to give you a down-payment?

Mass market appeal is tough to get. Pebble arguably never got there, but Coolest Cooler arguably has. They are the two most successful kickstarter projects ever and both achieved 62-68k backers. But mass market appeal? I'd give it to Coolest.

One final thought on crossing the chasm is that it's easier with product iterations. Version 1 might suit the early adopters, V2 might earn higher market share among the early adopters, V3 might be where you start to see mainstream sales starting. Each product needs to improve and adjust to customer feedback.

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Happy to go into more detail on a call.