On this day 30 years ago, the wall confining East Germans to state surveillance, centralized control, and economic deprivation gave way to freedom.

The Berlin Wall offered us a natural experiment—one that showed which political system best enables people to thrive and flourish. East and West Berlin gave us a tale of two cities, made up of similar people with a shared history and culture who, once divided by the wall, led quite dissimilar lives.

I grew up in West Germany. After the fall of the wall, many families left the East to seek a better life in the more prosperous West. Many of my schoolmates were among those who had traveled west.

One of these classmates was Romy. She was tall and had long, brown hair down to her hips. And she loved bananas.

Bananas had always been abundant and cheap during my childhood in West Germany. Those of us who grew up in the West simply took them for granted.

For Romy, however, being able to eat as many bananas as she wanted, whenever she wanted, was one of the defining characteristics of living in the West.

Behind the Wall, bananas were something of a rare luxury good, she told us. On days when stores got a shipment of bananas, everyone could tell by the long lines out the doors. Often her mom would stand in line for naught, finding all bananas had been sold before it was her turn.

To this day, when Germans in the east see a long line, they will often say, “Do they have bananas here or why is the line so long?”

Scarcity versus abundance is one key contrast that separates socialist countries from economically free countries.

People living in democracies that prize individual liberty, respect private property, and allow markets to operate freely typically enjoy abundance. They can get plenty of bananas cheaply, even if they are grown elsewhere.

The free-enterprise system is the most effective means of delivering goods and services that satisfy people’s preferences.

By comparison, people whose economic freedoms are oppressed in the misguided pursuit of some centrally directed, socialist economy, suffer scarcity.

In communist East Germany, it meant that people came to view the simple banana as a rare, exotic treat. In today’s socialist and corrupt Venezuela, it means people are reduced to making a whole meal of nothing but homegrown bananas.

Mealtime in Venezuela is increasingly restricted to cassava or bananas due to a shortage of meat—a product subject to strict price controls. Hunger and malnutrition are on the rise. Venezuelans reported an average weight loss of 24 pounds in just one year, 2017, which some call the “Maduro diet.”

Centrally controlled economies destroy incentives to work and invest. They also short-circuit important market signals about what and how much to produce. All of this leads to scarcity and waste.

Another glaring contrast between these two political systems is whether people are free to exercise their individuality, to speak their mind, and to travel—or whether they are subject to government dictates, persecuted for dissent, and held captive.

A high level of individual freedom is characteristic of free-market democracies. East Germany, on the other hand, erected a massive surveillance system to ensure conformity among its population. The goal was to prevent anyone who had not fully embraced the idea of being under the near-complete control of the state from exercising basic individual rights, including the freedom to disassociate by leaving.

In addition to the government’s official spy apparatus, many East Germans took it upon themselves to do their “civic duty” by telling on their neighbors and friends.

By appealing to human vices such as envy and jealousy, and by glorifying the state above the individual, socialism brings out the worst in people. Under socialism, the ends justify the means, regardless of how brutal and evil they may be.

Thirty years on, many democratic market economies, including Germany and the United States, are experiencing a resurgence of socialist politicians.

Today, as then, they promise glorious social programs and greater equality by restricting markets and confiscating wealth. Unfortunately, this magical thinking appeals to many who feel left behind, as well as younger people who have not seen the harsh reality that comes of socialism.

Germany’s history is just one powerful reminder that socialism does not work. It has failed wherever it has been tried. Instead of prosperity and security, it inevitably delivers decline, despair, and serfdom.

Free people everywhere would be wise to study life behind the Berlin Wall to avoid repeating the mistakes of the past.