Those who choose to focus on passive income will need either family money, funds from investors, or the nerve to borrow large sums by taking on debt to fund the purchase of assets. Consider someone who takes out substantial bank loans to build an apartment building or buy rental houses. Although this can turn a very small amount of equity into a large cash flow stream, it is not without risk. When using borrowed money, the margin of safety is much smaller because you can’t absorb the same degree of setback before defaulting and finding your balance sheet obliterated.
The underlying idea is that investors require a rate of return from their resources – i.e. equity – under the control of the firm's management, compensating them for their opportunity cost and accounting for the level of risk resulting. This rate of return is the cost of equity, and a formal equity cost must be subtracted from net income. Consequently, to create shareholder value, management must generate returns at least as great as this cost. Thus, although a company may report a profit on its income statement, it may actually be economically unprofitable; see Economic profit. It is thus possible that a value deemed positive using a traditional discounted cash flow (DCF) approach may be negative here. RI-based valuation is therefore a valuable complement to more traditional techniques.
Residual income is the amount of net income generated in excess of the minimum rate of return. Residual income concepts have been used in a number of contexts, including as a measurement of internal corporate performance whereby a company's management team evaluates the return generated relative to the company's minimum required return. Alternatively, in personal finance, residual income is the level of income that an individual has after the deduction of all personal debts and expenses have been paid.