In a market, the price of something settles where the quantity people want to buy equals the quantity sellers want to provide. If a product is scarce and many want it, buyers bid the price up; if it's abundant or few want it, sellers cut prices to move it. This constant tug is supply and demand, and the price it produces is a signal that coordinates strangers who never meet.
That signal does real work. A high price tells producers 'make more of this' and tells consumers 'use less of this'; a low price does the reverse. This is what Adam Smith meant by the 'invisible hand' — no central planner decides how many umbrellas a city needs, yet prices nudge production and consumption toward rough balance. Interfering with the signal has consequences: price caps below the market rate reliably cause shortages, because they tell producers to make less exactly when demand is high.
In 1973 and again in 1979, the US government capped gasoline prices to protect consumers during oil supply disruptions. The result was the opposite of the intent: because the capped price sat below what the market would have set, it told refiners and station owners it wasn't worth supplying more, and it told drivers there was no reason to conserve. The predictable outcome was hours-long lines at gas stations, stations running dry, and rationing by odd-even license plate days. The scarcity wasn't caused only by the oil shock — the price control turned a shortage of oil into a shortage at the pump by disabling the signal that would have rationed supply and spurred more of it.