"Conferences have this diminishing return going on, " says Marci Alboher, an Encore.org vice president who speaks at dozens of conferences a year.

WSJ: Are Retirement Conferences Worth It? | WSJ.Money Summer 2013

He acknowledges that serialized dramas like The Shield may wear out their welcome and offer a diminishing return if they continue to run.

FORBES: There Is No Box

The hiatus caused by starting a family at this stage could then prove a setback professionally, diminishing the return on investment.

ECONOMIST: Constitutional questions

At this point, IT managers say, the return on investment is rapidly diminishing: Even a sizable bonus can't compete with the permanent pay raise a year-2000 worker can get by jumping ship at this late hour.

CNN: Managers turn away from retention bonuses for Y2K

And they create new opportunities to make high-return investments in increased complexity before those diminishing returns again set in.

FORBES: Why Start-ups Matter

Its five-year average return on capital of 15% shows no sign of diminishing.

FORBES: No Fashion Victim

Diminishing equity value across the broadcasting and publishing industries means they will not return without a good deal more dilution and debt restructuring.

FORBES: Forecasts

All of which is to say that central banks have to a large extent displaced the market, providing record volumes of loans to banks, and in return for assets or collateral of increasing diversity and - arguably - diminishing quality.

BBC: Should JP Morgan have listened to Winters?