A consumer of a single commodity is in equilibrium when

A consumer of a single commodity is in equilibrium when they have reached a point where they are satisfied with the amount of the commodity they have purchased and consumed, and do not feel the need to buy any more or any less of it. This equilibrium can be achieved in different ways, but one common way is when the marginal utility, or the additional satisfaction gained from consuming one more unit of the commodity, is equal to the price paid for that unit. In other words, the consumer is willing to pay the price because they feel they are getting enough satisfaction from the additional unit. At this point, the consumer has no incentive to buy more of the commodity, because the marginal utility would be lower than the price, and they would feel like they are overpaying for the satisfaction gained. Conversely, if the price were to decrease, the marginal utility would be higher than the price, and the consumer may feel like they are getting a good deal and may want to purchase more of the commodity. Ultimately, the consumer is in equilibrium when they have found a balance between the satisfaction gained from the commodity and the price paid for it.