As interest rates have been going down over the past 30 years, bond prices have continued to go up. With the 10-year yield (risk free rate) at roughly 2.55%, and the Fed Funds rate at 1.5% (two more 0.25% hikes are expected in 2018), it’s hard to see interest rates declining much further. That said, long term interest rates can stay low for a long time. Just look at Japanese interest rates, which are negative (inflation is higher than nominal interest rate).
Here's another example. If a person owns apartments that are rented out at a profit, they earn money each month without working a specific number of hours. If the owner earns $100/month net income from each apartment, the determining factor is how many apartments they own, not how many hours they work. Therefore, they may own 1 apartment and make $100 net income each month, or they could own 500 apartments and make $50,000 ($100 per apartment) each month.
Residual income models of equity value have become widely recognized tools in both investment practice and research. Conceptually, residual income is net income less a charge (deduction) for common shareholders’ opportunity cost in generating net income. It is the residual or remaining income after considering the costs of all of a company’s capital. The appeal of residual income models stems from a shortcoming of traditional accounting. Specifically, although a company’s income statement includes a charge for the cost of debt capital in the form of interest expense, it does not include a charge for the cost of equity capital. A company can have positive net income but may still not be adding value for shareholders if it does not earn more than its cost of equity capital. Residual income models explicitly recognize the costs of all the capital used in generating income.
In equity valuation, residual income represents an economic earnings stream and valuation method for estimating the intrinsic value of a company's common stock. The residual income valuation model values a company as the sum of book value and the present value of expected future residual income. Residual income attempts to measure economic profit, which is the profit remaining after the deduction of opportunity costs for all sources of capital.