What happens in an environment - such as the one we are in currently - that is characterized by prolonged periods of low volatility? One of the effects of diminished price swings is the decline in return expectations. As an example, the chart below shows the spread demanded by investors in US high yield bonds vs. the volatility of total returns in that market.
This low volatility regime originates from the policies of major central banks, policies that have been both highly accommodative and relatively transparent - at least in the intermediate term. And any market conditions that are viewed as a form of tightening or rising uncertainty are often met with further accommodation. This is particularly true in the US. For example the markets' negative reaction to the Fed's looming taper last year was met with a delay and a reduction in taper's size ("small taper"). The risk that monetary policy will materially deviate from markets' expectations without the Fed making an accommodative adjustment has diminished significantly, resulting in lower volatility across the board.
Some have suggested that this Fed-engineered muted volatility regime is precisely the reason for low real interest rates. The reduced uncertainty around monetary policy trajectory results in lower volatility in fixed income markets, dampening return expectations. These lower return expectations mean that investors are willing to live with lower coupon in return for smaller swings in the value of their investments.
Deutsche Bank: - If pre-crisis rules for financial engagement [Fed's involvement in the markets] raised both the volatility in the economy and the return in the economy, then reducing that volatility should reduce economic return. QED: the real rate of growth may be permanently both more stable and lower. … Returns in fixed income may depend progressively less on price and more on income.
The other effect of operating in a low volatility regime for prolonged periods is increased risk taking - often in the form of higher leverage. We've seen this manifested in higher NYSE margin debt and growing leverage of LBO transactions for example. Janet Yellen however continues to downplay the potential for asset bubbles and other threats to financial markets resulting from low volatility. The view at the Fed is that, at least for now, financial stability can be achieved through regulation - including containing asset bubbles. That assumption of course remains to be proven, given some of the past failures of sophisticated financial regulation (see example).
For now the markets have faith that regulation will indeed maintain financial stability in the face of highly accommodative monetary policy and low volatility. And as the low volatility regime becomes the norm, return expectations decline across the board and investors become lulled under the warm blanket of asset price stability provided by the central banks.