Speaking to your audience should be an ongoing process throughout the lifetime of your product.
An open dialogue with members of your target audience or active users of your product will do one of two things; Validate assumptions you already had, or give you insight you hadn't thought of. Either way, it's an valuable practice any start-up should embrace.
The great journey
Think of the lifecycle of your product as a journey. You may have the destination in mind, but you would be wise to use the insight of others before setting off into uncharted waters...
Before you set sail, ask if anyone else has been in the direction you intend to head to, check the map, is it unexplored territory or an established trade route? Ask around for tales of others that have set off in that direction only to never be seen again.
You may quickly find out your map just hasn't been updated, and a settlement has long been set up there, killing your dreams of trailblazing before you even begin. Maybe you'll hear tales of lost treasure waiting for someone canny enough to reach out and claim it, but if you don't bother to ask how will your ever know. It would be foolish to simply set off in a random direction, just as it would be foolish to build a product without speaking to your audience.
Once you've built your minimum viable vessel and made it clear to all which direction you intend to go, others may want to join you - explorers, adventurers, or any who stand to gain from your venture. These passengers are your first users, and their input will be your most valuable lifeline in staying the course.
Use the expertise and experience of those who have sailed similar waters. If most of your crew is telling you there is a hole in the ship, it might be worth listening. Be sure not to lock yourself in the captain's quarters and assume you'll all arrive safely - make sure there are clear communication channels between you and those who are on the journey with you.
Even if you do arrive at the golden shores of PMF - do the settlers like the new town hall you built them? Or did you just drain all of your resources into a feature that, you thought would be cool, but ultimately serves no purpose.
In the end it's your journey, but at all stages, open dialogue will serve to keep you on the right path and mitigate as many mistakes as possible.
Communication is key
In the early days, getting out in front of potential customers is going to help you find out; if the problem is even real, what the current market solutions are, and if there is a desire for your solution at all.
Just because you identify a problem, it doesn't mean anyone wants to pay you to fix it.
Once you're up and running, there is no better resource for feedback than the people using your product every day. While you cannot satisfy every wish your customers may have, ignoring their input will push users to stop pointing out otherwise key issues, or worse, leave your platform altogether.
If you're not listening to your users you will likely end up building things nobody is asking for while leaving already broken features by the wayside.
Maintaining open channels of communication, alongside intelligent and sensible processing of the feedback, is the best way to build trust and loyalty with your users, promote healthy growth and build a product or platform people want to use.