# What Is Complexity?

While it seems more and more common these days, it’s important to determine when you’re operating in complexity. Complexity means that little things can have a big effect and big things can have no impact. Complexity also renders some of the ways we think about problems as useless, at best.

In The Black Swan: The Impact of the Highly Improbable Fragility, Nassim Taleb writes:

I will simplify here with a functional definition of complexity—among many more complete ones. A complex domain is characterized by the following: there is a great degree of interdependence between its elements, both temporal (a variable depends on its past changes), horizontal (variables depend on one another), and diagonal (variable A depends on the past history of variable B). As a result of this interdependence, mechanisms are subjected to positive, reinforcing feedback loops, which cause “fat tails.” That is, they prevent the working of the Central Limit Theorem that, as we saw in Chapter 15 , establishes Mediocristan thin tails under summation and aggregation of elements and causes “convergence to the Gaussian.” In lay terms, moves are exacerbated over time instead of being dampened by counterbalancing forces. Finally, we have nonlinearities that accentuate the fat tails.

So, complexity implies Extremistan. (The opposite is not necessarily true.)

Based on this definition, complexity highlights some of the flaws in the way we approach things and inductive reasoning.

How do we know what we know? How do we know that what we have observed from given objects and events suffices to enable us to figure out their other properties ? There are traps built into any kind of knowledge gained from observation.

Consider the Turkey that is fed every day.

Every single feeding will firm up the bird’s belief that it is the general rule of life to be fed every day by friendly members of the human race “looking out for its best interests,” as a politician would say. On the afternoon of the Wednesday before Thanksgiving , something unexpected will happen to the turkey. It will incur a revision of belief.

If the hand that feeds you can wring your neck, you’re a turkey.

If you haven’t read it already, The Black Swan: The Impact of the Highly Improbable Fragility, is a must-read.