All of us need other people to supply the goods and services we have come to depend on. But we also need people who will pay us for the goods and services that we can supply, thus providing the money we require to pay those who supply our wants. In more primitive times, people were often forced to provide for all or almost all of their wants through their own effort. And so the same individual might have to make his own clothes, grow his own food, build his own house, and so on. A market economy permits people to specialize in those things they do best.
Some people are better at plumbing than they are at teaching philosophy.
Some are better auto mechanics than preachers. This specialization enables most of us to do a better job with our time and effort. But this specialization also increases our dependence on others. While it sometimes happens that the supply of some good may be too great or too small, these occasional glitches in the system are short-lived. It is worth pondering why, in a free market system, goods and services are usually available in a supply sufficient to take care of people's wants.