This is a more general answer, and in my opinion this question is asked to often by people new in startups, not implying that this is the case for you.
Ideas are like seeds, you need to nurture them to make them grow. And ideas are nurtured with work and decisions. To finish the product you need to make hundreds or maybe thousands of decisions, and each little decisions will make a big or small impact on the finished product.
The hard part is not finding the seed, it’s making the right decisions to nurture it to a great product.
And to succeed with this you need to build a great team and put a lot of hard work into it.
You mental model of the product you want to create today is not what the finished product will look or function like. It will be something else.