Parkinson's Law. Work expands so as to fill the entire time for its completion
Good article by Shane Parrish on Parkinson's Law:
Work expands so as to fill the time available for its completion.
But what I enjoyed most of the article was the sample meeting exemplifying Parkinson's Law of Triviality:
The time spent on any item of the agenda will be in inverse proportion to the sum [of money] involved.