Vapor–liquid equilibrium

Vapor-liquid equilibrium is like a see-saw game. It occurs when two different states (vapor and liquid) of a substance such as water are balanced and neither is more dominant. It's like two kids on a see-saw, both with the same weight, so the see-saw stays balanced. That's how it works with vapor-liquid equilibrium too - the two states of matter are balanced. Once the balance tips in one direction, the other one decreases and vice-versa.