Wealth concentrates not because the wealthy work harder, but because capital compounds and labour income doesn’t.
Inequality is usually argued about as a question of individual fairness: did the wealthy earn what they have, or extract it unjustly? That framing treats concentration as a matter of conduct, something that could in principle be fixed by everyone behaving better. It skips a prior, structural possibility: that certain financial arrangements concentrate wealth as an arithmetic consequence, regardless of how fairly any single transaction is conducted.
Wealth concentration names that structural effect: the tendency, over time, for wealth to accumulate in the hands of people who own capital rather than people who supply labour. This is a different question from capital allocation, which asks where money gets directed among competing uses in the moment (investment, savings, debt repayment). Wealth concentration asks who ends up holding more of the total as those flows repeat, year after year, an accumulation question, not an efficiency one. The clearest everyday mechanism runs through interest: every interest payment on a loan is a transfer from a borrower, typically someone working for wages to fund a mortgage, a business, or consumption, to a lender, typically someone with capital to spare. Multiplied across millions of loans and compounded over years, this is not a transfer that evens out. It is a one-way channel, moving money systematically from the working, labouring population to the capital-owning population, because only one side of the transaction is paid simply for holding money rather than for producing anything with it.
French economist Thomas Piketty documented the same logic at the scale of whole economies in Capital in the Twenty-First Century (2013): when the return on capital (r) persistently exceeds the overall rate of economic growth (g), wealth accumulated in the past grows faster than the wages and output produced in the present. Past wealth mechanically outpaces earned income and concentrates further, absent some outside shock or deliberate redistribution. Interest is one specific, everyday channel through which the same r greater than g logic runs: an economy where debt and the interest owed on it compounds faster than real output can grow concentrates wealth toward lenders even when every individual loan is repaid exactly as agreed.
Source: Piketty, T., Capital in the Twenty-First Century, Harvard University Press, 2013.