Science & TechMental model
Disturb a system at equilibrium and it pushes back.
Henry Le Chatelier stated in 1884: change the pressure, temperature or concentration of an equilibrium and it shifts so as to partly counteract the disturbance. Example, ammonia synthesis: more pressure drives the reaction towards the side with fewer gas molecules. Paul Samuelson carried the principle into markets in 1947: supply and demand respond more sluggishly short-term than long-term.
Useful: With any intervention in a stable system, expect a counter-movement that makes the effect smaller than planned.
Source: en.wikipedia.org