Central banks are making the same mistakes that led to the 2008 financial crisis
And the International Monetary Fund has taken this maxim to heart in its report on the global economy ahead of the G-20.
In it, the IMF gives 10 reasons for the central bankers in the world's biggest economies to keep interest rates at record lows.
These range from record low commodity prices, and weakening growth in China to low productivity in Western countries.
They're all pretty worrying and form the basis of a plea to keep monetary policy free and easy. Raising rates now would only make this worse, argues the IMF:
In most advanced economies, output gaps are still substantial, inflation is expected to remain below target, and monetary policy remains constrained by the zero lower bound. The expected boost in economic activity from lower oil prices has not materialized, and lower energy costs are keeping inflation low. Hence, monetary policy must stay accommodate to prevent real interest rates from rising prematurely.
The report is important because two of the big central banks, the US Federal Reserve and the Bank of England, have warned the market that they should expect rates to rise soon.
In the case of the Fed, while this could be as soon as this month, market turmoil is making the prospect of a rate hike less likely according to Citi:
Analysts have been debating about how much the Fed really cares about movements in the market, but we'll only know for sure when the central bank publishes its decision on September 17.
Or as Bank of America Merrill Lynch puts it: "If they don't hike, it's an admission that Wall Street threatens to reverse the recovery on Main Street."
The IMF's reasons, and the market turmoil, highlight one of the big psychological problems with central bank policy at the moment - There's never going to be a perfect time to raise rates.
There'll always be a market that's volatile, or a country in distress or an economic indicator that disappoints, which will make rocking the easy money boat unpalatable. But these are short-term factors.
It's a quirk of the brain known as myopic loss aversion. The short-term incentives to keep rates low are more powerful than the medium-term ones that suggest a hike is necessary, because people associate low rates with decent economic growth.
This is good marketing from the loose policy team, but ultimately hard to prove as these charts from BAML show:
There's always going to be a reason to keep rates low, even during benign economic times. It was one of the mistakes the Fed made before the 2008 financial crisis.
The problem, as we all found out along with Alan Greenspan, is that low rates can also be associated with financial instability which hurts growth more than low rates help.
The build up of the housing boom and bust, which kicked the banks and led to the crisis response of even lower rates, was caused in part by 12 rate cuts after 2001 from 6.5% to 1%. The short term boost to the economy was wiped out by the financial collapse in the medium term.
And we're back there again.
Low rates force money managers to take extra risk to get a decent yield on their investments. The OECD warned in June that this has led to investors seeking looser terms on deals (covenant protection) in return for better rates.
It's a mark of desperation. Low rates knock out a lot of financial business models that need a historically normal base rate to work.
Bond guru Bill Gross said it best on Wednesday:
"The Fed is beginning to recognize that 6 years of zero bound interest rates have negative influences on the real economy - it destroys historical business models essential to capitalism such as pension funds, insurance companies, and the willingness to save money itself."
The next financial crisis might not happen in the banking sector, but rather the insurance and fund industry. These guys are responsible for about $100 trillion of assets according to the OECD report so, if and when it happens, everyone will feel it.
While the debt markets react instantly to central bank policy, it generally takes about 12 to 18 months for an effect on the real economy.
Who knows whether the Brent crude oil price will still be hovering around $45-$50 a barrel in 2017, or $100. Or if China will be in full meltdown mode then or not. Or if Britain will be booming or in a recession.
They're obvious and scary but shouldn't take precedence over less obvious and scarier things when considering a rate rise.