Why do prices change?

A price does not move on its own. Every new number is a new handshake. For a number to change, somebody has to have agreed on a different one.

The thing being bought and sold is called a product. A day rarely holds a single agreement: for the same product, hundreds of people can be buyers and hundreds sellers at the very same moment. The crowd where they meet is called a market. Agreements happen there constantly, which means new numbers constantly.

When we say "the price" of a product, what we usually mean is the number of the most recent completed agreement; that one is called the last price. The next agreement may land on a different number, and at that moment the price has changed.

A number tells you what, never why. No number will ever write down for you why the price went to 5,400 — hunting for causes is the job of a different kind of information, and nothing in this course will hand you one. The answer to "why" may exist somewhere, but that somewhere is not this list of numbers; ask a number for its reason and the reason you get is the one you invented.