Language and the Pareto Principle.
The Pareto Principle was so named by Joseph M Duran the father of modern quality management.
Millions of managers rely on this principle to help separate the "vital few" from the "useful many" in their activities. This is commonly referred to as the 20-80 principle.
Vilifredo Pareto observed that in the majority of situations 80% of results can be attributed to 20% of the causes. This principle has been shown to apply in a variety of situations, from sales, to manufacturing, to management.
This principle applies equally when learning a language. From a possible vocabulary of over 250,000 words, 50,000 will give you mastery. Using the same ratio we can further reduce that to 10,000 words for conversational fluency and to 2,000 for communicative competency. The idea is that the amount of vocabulary that is necessary is far below the amount of vocabulary that actually exists.
The key is focus.
The Pareto chart is one of the seven basic tools of quality control. The purpose of the Pareto chart is to highlight the most important among a (typically large) set of factors. In quality control it often represents the most common sources of defects, the highest occurring type of defect, or the most frequent reasons for failures, rejections or customer complaints, and so on.
When focusing on improving your language in both the short and long term it is important to concentrate your efforts on the 20% which will give you the maximum results. Constructing your own language Pareto chart will give you a roadmap to follow providing you with a visual reference and the tool to manage your language progress.