Inertia

Newton's first law, as stated in the Principia (1687), says that every body perseveres in its state of rest or of uniform straight-line motion except insofar as it is compelled to change that state by forces impressed on it. Inertia is the name for that perseverance, and Newton defined it among the technical terms at the front of the book. What was new was the reference to impressed forces: motion needs no cause to continue, only to change. A puck on ice keeps sliding not because something pushes it but because nothing stops it. Mass measures how much force a given change requires, which is why the same shove moves a bicycle and barely troubles a bus.

The transfer is to systems that keep their state for lack of a force, not because the state is good. Samuelson and Zeckhauser gave 486 business and policy students the same investment choices with one option framed as what they already held, and that option was picked more often. They then found the pattern in the field: Harvard employees who had enrolled in a health plan before 1980 stayed with the incumbent Blue Cross plan at two to four times the rate of new employees of the same age choosing from the same menu. Madrian and Shea found the same with retirement savings: switching a company's 401(k) from opt-in to automatic enrolment raised participation, and a substantial share of new hires then kept the default contribution rate and fund. Defaults, habits and legacy systems persist because changing them takes a force nobody is applying.

The analogy has limits. An institution is not a body in a vacuum; it keeps its state because people are choosing it, out of fear of loss, attention costs, or the fact that the current arrangement is someone's job. Those are reasons, and reasons can be argued with, whereas a puck cannot. Status quo bias also sometimes points the right way: the default was often set by someone who knew more than you, and Chesterton's fence applies. The useful habit is to notice when 'we have always done it this way' is doing all the work in a decision, then ask what force would be needed to move it and who would have to apply it.