Homeostasis
Homeostasis describes the tendency of systems — biological, organizational, and social — to resist change and actively work to maintain a state of internal equilibrium. Originally a biological concept (the body's maintenance of stable temperature, blood pH, blood sugar), it has broad applications to understanding why organizations resist change, why habits are hard to break, and why complex systems often return to their prior state after interventions.
Nash Equilibrium
A Nash Equilibrium is a set of strategies in which no player can improve their outcome by unilaterally changing their own strategy, given what the others are doing. Named after mathematician John Nash, who proved that every finite game has at least one Nash Equilibrium, it is the central solution concept in game theory and explains stable outcomes in strategic interactions — not necessarily optimal, but stable because no one has individual incentive to deviate.