You may or may not have to finish the last 20%. Since the whole article is based on the premise that you have to, it fails for me.
There are attributes of your project that are table stakes (absolutely required to compete) and there are regulatory or safety requirements. You need all those to ship.
However, everything else is “value” or even just “perceived value” and it is up to your customer which ones “you have to do””.
Let’s put the 80/20 rule another way. If I can get 8 out of 10 features in 20% of the time, it makes sense to do those 8 ( assuming they all have at least some value ).
But what do I do with the 80% of the effort that it would take to get the last two features?
The answer is opportunity cost. What could I do with that time instead? Put another way, what am I NOT going to be able to accomplish because I chose to add those last two features?
If the answer is that I have other features that customers value more, I should do those instead. If I have a backlog of features that all take the same effort as the first 8. I can do 32 of them in the time it would take to deliver the original 2!!
The statement was made that “customers do not like to use 80% of a website”.
If I read this article, maybe I implement the full 10 original features. If I embrace 80/20, maybe I implement 40 instead. Hey look, the “just do 100%” approach resulted in a website with 25% as many features as 80/20. If “customers do not like 80 percent of a website”, they are probably even less happy with 25%. Right?
Now, not all features have the same value. So, the math is not as simple as above. But, in my view, this is the right way to think about 80/20. The perfect is the enemy of the good.
So that tue perfectionists can hate me even more, the same is true “within” features (or whatever other axis you are evaluating). Sometimes customers “expect” or even “demand” features they do not really use. Compliance is a an example. Or stuff that used to matter in a product category (and is still used as a filter) not really does not anymore. You can get a lot of value in your product by adding this stuff, but it is a waste of resources to “do it right” or match every competitor like for like. You may find again that you get essentially all the market success “value” from doing some fraction of the work. Note, I am not saying to ship stuff that is buggy or stuff that does not really work. If that is what you think I am saying, you misunderstand. A shorter version may to say “build what your customers will actually use and not much more”.
What you really want to spend your time on is the stuff that excites people, that differentiates your offering, and takes “relatively” little effort to execute. That is probably not “the last 20%”, most of the time.