If Nassim Nicolas Taleb's black swans are geopolitical bolts from the blue (or "unknown unknowns"), then their grey cousins are the known unknowns. We can see them coming, but their impact is just as unpredictable.
We have been using the grey swan metaphor for a while now in our financial reporting to describe the bewildering array of risks currently facing global business ? risks that act as a significant drag on confidence and thereby hold back economic expansion worldwide.
GDP growth appears stuck at around 3% real or 5% nominal, with little sign that it will break out from this limited growth pattern any time soon.
Although we remain unabashed bulls on the BRICs and Next 11 ? and the faster growth markets in Asia, Latin America, Africa, the Middle East and Central and Eastern Europe are still growing more quickly than the slower markets of North America and Western Europe ? they have lost some of their sheen (in the short-term) as Russia, Brazil and China have all cooled. Only India is growing strongly, still reflecting Modi-optimism.
The other grey swans causing anxiety in multinational boardrooms include the ongoing crisis in Ukraine and consequent sanctions regime; the various interlocking conflicts and terrorist activities across the Middle East and North Africa; the increasingly dysfunctional relationship between Greece and what remain ? for now ? its EU partners; and the continuing concerns about the scale of the US deficit.
Also flapping menacingly towards us is the prospect of the Federal Reserve tightening US monetary policy ? and its unpredictable impact on bond and equity markets. While interest rates will remain low for a long time yet, recent stock market gyrations suggest the effect of any increase could be severe.
Another, more parochial, destabilising factor is the upcoming UK referendum on British membership of the European Union ? a by-product of the unexpectedly decisive Conservative victory in the General Election. Regardless of the outcome, this will create significant uncertainty and lead businesses to defer investment decisions. The best case scenario is that it will be neutral for the UK economy.
These grey swans give boards ? already super-conservative in the post-Lehman era ? even more reasons to rein in spending. Low inflation and fears of deflation mean brands have little or no pricing power, and activist investors focused on short-term horizons hardly encourage expansionary thinking.
The inevitable result is an understandable but excessive concentration on cost management, with finance and procurement (not growth-driving functions like marketing and product development) in the box seat.
If you are trying to run a legacy business, at one end of the spectrum you have the disrupters like Uber and Airbnb, and at the other end you have the cost-focused models like 3G in fast-moving consumer goods and Valeant and Endo in pharmaceuticals. In the middle, you have the activists led by Nelson Peltz, Bill Ackman and Dan Loeb, stressing short-term performance. None of which creates a positive environment for the calculated risk-taking required for top-line growth and long-term success. In 2014, the S&P 500 paid back more in dividends and share buybacks to share owners than their combined retained earnings.
And while some institutional investors, notably the world's most powerful fund manager Larry Fink at BlackRock, have said publicly that they are tiring of such short-termism, we do not expect this corporate behaviour to change in the coming years.
Amidst the gloom, however, there are reasons to be cheerful. Countries like Indonesia, the Philippines, Vietnam, Egypt, Nigeria, Mexico, Colombia and Peru are encouraging, as is the albeit mild recovery in Western Continental Europe, chiefly in Germany, Spain and Italy. The UK economy has been a bright spot, especially for WPP.
Also giving rise to (cautious) optimism are Iran and Cuba ? each poised to make a return to the international community and open their doors to global trade, as Myanmar did two years ago, and Vietnam even longer ago. Although very different in nature and size, each has the potential to become a significant consumer market.
Not long ago this would have seemed impossible, reminding us that unexpected geopolitical developments with uncertain outcomes are not always something to be feared ? and that grey or black swans can whiten.
Sir Martin Sorrell is the Founder & CEO of WPP.