Parkinson’s Law states that the amount of time you give a task to take is equivalent to the amount of time that task will take. In other words, the work fills up the time allotted for it. For example, if you have a week to finish an article, the article will take all week to finish. Basically, the more time you have available to complete the task, the more time you will spend doing it.
In 1955, Cyril Parkinson, a British military historian, published a satirical article in the British magazine The Economist, in which he stated the empirical law: "Work expands to fill the time available for its completion". In this article, he talked about how organizations have uncontrolled growth because of their self-serving nature: each department creates work for the other. The official wants to multiply subordinates, not rivals. Cyril Parkinson later promoted his idea in a book "Parkinson’s Law: The Pursuit of Progress". Despite its satirical origins Parkinson's statement is true today.
Tips & Tricks
If the task takes a long time, try to do it with more quality.
Avoid prolonged perfectionism of the result. The more alternatives and improvements you offer, the more you add to the task and do more work. Focus on a workable result.
Set goals and define clear criteria, otherwise the task can become exhausting and long.
Set tight deadlines for your project. This will help you spend exactly that amount of time working and improve your productivity.
Stop working late. If you apply Parkinson’s Law and condensed your working hours to a shorter or at least regular workday then you'll increase your ability to focus and become more productive.
Use Pareto Principle to your advantage. Look at everything that involved in the process and identify the most important elements. Then focus your time on tasks that actually matter.
Track your time. To identify your critical tasks you have to know exactly how you're spending each hour of your day.