Every economy builds on some measure of scarcity. While capitalism, even a mixed market model, has its rich and poor, it is also the only economic model that fosters a burgeoning, healthy middle class, while communism in the end makes everyone poor, as is the case in Venezuela. Without scarcity, however, there is no desire to acquire what businesses offer, as everyone seeks subsistence. With scarcity, people will buy what they can't get themselves and everyone participates in specialization, providing others with what they need or think they need Meeting scarcity's and thus consumer demands, fosters opportunity and mobility, as consumers become accustomed to paying the costs that private providers set. These costs, like scarcity itself, are fluid, due to consumer habits, providing even greater opportunity for economic health and gain, leading to some trade-offs regarding like valued items and services, as in a barter economy, which is not economically mobile and fluid, but just quid pro quo, that is, "this for that." Trade-offs that are non-barter based, however are useful realizations that certain commodities and services have like value, but are best paid for with monetary means. Other tradeoffs come from the recognition that while the consumer must pay for everything, businesses are enabled to produce new products for their consumption, which further fuels the economy.