The 80 / 20 Rule
The idea behind the 80 / 20 rules is that 80% of the effects of any given process come from 20% of the effort put into it. This is called the 80 / 20 rule or the Pareto Principle. What this means in UX is that 80% of our users uses 20% of our features and 20% of our code causes 80% of the errors. Another way to look at is the that a small number of things have a significant impact.
Perfection favors the designer not the user. When designers add features without thought, they are inadvertently shooting themselves in the foot. Designers who strive for perfectionism can harm their team. This can have a potentially negative effect on the user. A user is not looking for perfection as much as something functional that helps them achieve their intended goals. When UX designers are blind by perfection, there is no room to look at the critical 20% that has the more significant impact.
User experience designers can waste precious time fixating over minutiae that can have little to no impact or a negative one. Adding features invariably adds complexity, and this complexity does not lend itself to a high quality user experience.
Build the thing you want to build with the least amount of features to engage early adopters. Once we have got those early adopters, we can start to learn from them and use this research to develop your product iteratively and incrementally. The Pareto Principle means we can identify the top usability issues that our users are experiencing. Knowing the problem our users are experiencing gives us the constraints to work within to design a solution. The Pareto Principle can help us prioritize what problems to solve. The principle will highlight the most pressing usability issues that are affecting the most significant number of people.