In 1960 South Korea was poorer than many African nations. Today it builds smartphones and ships for the world. That transformation came from one thing repeated for decades: economic growth — the sustained rise in an economy's output per person over time. Nothing else matters as much for how people live.
The engine behind it is compounding. Small differences in the growth rate explode over time, just like interest on savings. A country growing 1 percent a year takes about 70 years to double its income. A country growing 4 percent doubles in under 18 years. Run that gap for a century and the fast grower ends up with roughly 50 times the income of the slow one. Tiny rates, vast outcomes.
A handy shortcut makes this concrete. The rule of 70 says you can estimate the years it takes income to double by dividing 70 by the growth rate. Grow at 7 percent and income doubles in about 10 years. Grow at 2 percent and it takes 35. The rule turns abstract percentages into something you can feel.
To explain what drives growth, economists turn to the Solow growth model, the standard framework built around capital, labor, and technology. It tracks how an economy accumulates the tools and machines that workers use to produce.
The model rests on three forces. Saving adds new capital, because what people do not consume gets invested. Depreciation wears existing capital down, as machines rust and buildings age. As capital piles up, each new machine adds a little less than the last, a problem of diminishing returns. Eventually saving only just covers depreciation.
At that point the economy reaches its steady state — the level of capital per worker where new investment exactly replaces what wears out, so capital and output per person stop growing. This is the model's most famous and unsettling result. Pile up capital alone and growth eventually stalls.
So what keeps rich countries growing forever? Total factor productivity, the efficiency with which an economy turns capital and labor into output. Better technology, smarter organization, and new ideas raise output without needing more inputs. Unlike capital, ideas do not suffer diminishing returns, which is why technology is the true engine of lasting growth.
Newer theories build this in directly. Endogenous growth treats innovation as something the economy produces on purpose through research and education. And underneath it all sit institutions — property rights, the rule of law, and stable government. Without them, no amount of capital or technology takes root, which is why two neighboring countries can diverge so sharply.