Leverage

Imagine you buy a house for 100 million KRW (around $75,000) using only your own money. If home prices rise by 10% to 110 million KRW, you have earned 10 million KRW on your 100 million KRW investment. Your return on investment is exactly 10%.

Now, imagine you buy that same 100-million-KRW house using just 20 million KRW of your own money combined with an 80 million KRW bank loan. When the property value rises by 10%—yielding that same 10 million KRW gain—you pocket 10 million KRW after repaying the loan, all from your initial 20 million KRW down payment.

Even though the home's price rose by the exact same 10%, the return on your personal cash jumps from 10% to 50%—a fivefold increase (setting aside mortgage interest and taxes for simple math). However, this boost only happens if the asset appreciates faster than the cost of borrowing; if interest exceeds your gains, your losses multiply instead. This dynamic, where debt acts as a fulcrum to multiply your returns on equity several times over, is called the leverage effect.

A lever dramatically magnifies force, but if the weight crashes down the wrong way, the person holding the lever can be thrown violently into the air. Leveraged investing works the same way: while it generates handsome profits on the way up, losses spiral out of control just as fast on the way down.

Suppose that 100-million-KRW house purchased with 20 million KRW of your own savings and 80 million KRW in debt drops 10% in value to 90 million KRW. The property value dropped only 10%, but the 80 million KRW owed to the bank does not shrink by a single cent. Sell the house and repay the loan, and you are left with just 10 million KRW.

In other words, a modest 10% decline in the market instantly wipes out half (50%) of your initial principal. If prices fall by 20%, your entire 20 million KRW disappears. Drop any further, and selling the property will not even cover what you owe the bank, leaving you with underwater debt (negative equity). This is why leverage is widely known as a double-edged sword.

Leverage extends well beyond financial leverage—the practice of individuals or corporations using debt to boost returns on equity. Businesses also evaluate leverage embedded in their cost structure when building factories or purchasing machinery.

When a company carries high fixed costs (like factory upkeep) regardless of sales, but incurs low variable costs to produce each extra item, any small change in sales triggers a massive swing in operating profits. Higher sales send profits soaring, but a dip in sales can trigger steep losses. This is known as 'operating leverage.'

In South Korea's real estate market, 'gap investment'—purchasing a home with an existing tenant using their jeonse deposit (a large lump-sum lease deposit) as an interest-free loan—is another textbook example of leverage. Because that deposit must eventually be returned, dropping rental or home values can create 'tin-can jeonse' (negative equity where the landlord cannot repay the tenant), leaving both parties vulnerable. Ultimately, leverage describes any setup where borrowed money or fixed costs act as a lever to widen the swing of your outcomes, both up and down.