But none of the central bankers can make any such claim today, because for the time being at least, they have reached the limits of what they can do. They are all out ammunition.
The ECB has stopped intervening, and the US Federal Reserve is even busy unravelling the measures it has taken over several years. The improbable has thus become paramount again.
For example, the US economy is unlikely to go into recession in 2019. The same can be said of Europe, though the probability is higher.
But global leverage is so huge today that it could swiftly exacerbate a downturn. And if it did, the downturn would easily be worsened by any external shock that might occur – like a renewed escalation in US-China trade tensions, or a political crisis in Europe.
If that scenario came about, just how little room to manoeuvre central banks have left would become glaringly obvious.
Investors would then have to bear the brunt of such an unforeseen deterioration in the financial environment.
In other words, while a recession is still improbable, the challenges it would throw up if it took place have become much more daunting for investors.
It is mainly this kind of tail risk, which our omnipotent central banks had eliminated, that must be considered again going forward.
Didier Saint-Georges is managing director and member of the investment committee at Carmignac