the biggest issue usually between idea and execution is locating and actually reaching the market cost effectively and in a timely manner.
Suppose your product is for x people who like y.
Good. You have an Ideal Customer Profile.
Then you say, they will need my product when they do z. Those are the triggers. Meaning person has problem and knowledges problem and is actively looking for solution and at the set of a trigger they will do this.
So that now moves us into demand harvesting stage caused by a trigger (not demand generation which is missionary convincing a person they have a problem).
All good. Now all that was easy. The real hard part is reach. How will you find these folks?
Google is not enough. How will you access the hubs, the well connected early adopters to try your product/service and do word of marketing/referral for you for free?
I find in most of my sales jobs, reach is always the issue. Marketing is usually clueless. So I need to usually figure out clever ways to identify and reach this market.
Example from a recent consulting job. Mechanic wants to focus on Minivans since they are constantly used and constantly need repairs.
Ok who drives minivans: moms.
Ok which moms will be hubs early adopters? Moms that are on committees that will tell others so that will we will get word of mouth.
How to we do reach these moms - through their hair stylists.
What. Huh.
To go after your hub early adopters you need to find the people they will listen to and trust.
These high influential moms that will tell other moms are usually in charge of groups and constantly need to maintain their appearance. They regularly go to salons. They trust their hair stylist more than they trust their husbands.
Great: We designed a campaign to have hair stylists at select locations to try the mechanic's services at a deep discount. Immediately after trying our services, we gave them discounted coupons to give to 1 or 2 of their clients.
Then the these high connected (more like switches than hubs since they become to a number of groups) early adopter moms a chance to try us and subsequently tell their friends. Essentially the clairol commercial tactic with a twist.
Hope this helps. No time to make it shorter.
tldr: pick the one that easiest to reach the well-defined market that can purchase your product/service. And that has easily identifiable highly connected early adopters. This will make marketing easier and actually doable.