That's just yet another instance of the 80/20 rule (derived from the Pareto Principle).
In my industry (games) it's well known that 80% of the effort goes into the last 20% of the product, but also the last 20% of polish makes 80% of the quality.
> but also the last 20% of polish makes 80% of the quality.
I've noticed this, too. When a product is 80% of the way there, the people behind it see a product that's nearly done. Your audience, on the other, sees a piece of garbage.
The problem I've been running into is that my second version took 1 month to reach 80% "complete" and is taking 3 more months to finish that last 20%.