"It is of great use to the sailor to know the length of his line, though he cannot with it fathom all the depths of the ocean"

John Locke's quote is a metaphor for the importance of knowledge and understanding. It recommends that although we may not be able to completely understand the depths of a scenario, it is still advantageous to have a basic understanding of it. This is specifically real for sailors, who require to know the length of their line in order to navigate the ocean. Understanding the length of the line gives them a standard understanding of the ocean's depths, even if they can not completely fathom them. This quote is a suggestion that knowledge is power, and that even a fundamental understanding of a situation can be useful. It also functions as a tip that we need to never ever stop discovering and making every effort to comprehend the world around us.