The human brain processes a tremendous amount of information every single second. We do many things on some autopilot, driven by instincts and habits. Most of our daily routines are like this. Another area of brain activity is thinking, learning and decision making. Such actions are being performed significantly slower and require much more power than those automatic operations.

Dual process theory in psychology suggests that these types of brain activity are indeed entirely different and there are two different processed for two kinds of thinking. One is the implicit, automatic, unconscious process, and the other one is an explicit conscious process. Unconscious processes are formed for a long time and also very hard to change since changing such a process would require developing a new habit, and this is not an easy task. The conscious process, however, can be altered through logical reasoning and education.

These processes, or systems, happily co-exist in one brain, but are rather different in ways how they operate. Keith Stanovich and Richard West have coined the names implicit system, or system 1 and explicit system, or system 2 (Individual difference in reasoning: Implications for the rationality debate? Behavioural and Brain Sciences, 2000). Daniel Kahneman in his award-winning book Thinking Fast and Slow (New York: Farrar, Straus and Giroux, 2011) assigned several attributes to each system:

What all this has to do with DDD? Well, the point here is more about how we make decisions. The Cynefin complexity model requires from us at least to categorize the complexity we are dealing with in our problem space (and also sometimes in the solution space). But to assign the right category, we need to make a lot of decisions, and here we often get our System 1 speaking and making assumptions based on many of our biases and experiences from the past, rather than engaging the system 2 to start reasoning and thinking. Of course, every one of us is familiar with a colleague exclaiming yeah, that's easy! before you can even finish describing the problem. We also often see people organizing endless meetings and conference calls to discuss something that we assume to be a straightforward decision to make.

Cognitive biases are playing a crucial role here. There are some biases that can profoundly influence the decision making and this is positively the system 1 speaking. Here are some of the biases and heuristics that can affect your thinking about the system design, which you can recognize:

• Choice-supportive bias: If you have chosen a thing, you will positive about this choice despite your choice might have been proven to contain significant flaws. This is typical when we get to the first model and try to stick to it at all costs although it becomes obvious that the model is not optimal and needs to be changed. Also, such bias can be observed when one chooses a technology to use, like a database or a framework. Despite many arguments against using these the chosen technology, it will be very hard to make something that left a trace in the heart.
• Confirmation bias: Very close to the previous one, the confirmation bias makes you to only hear arguments that support your choice or position and ignore arguments that contradict your it, although these arguments may show that your position is wrong.
• Band-wagon effect: When the majority of people in the room agree on something, this something begins to make more sense to the minority that previously disagreed. Without engaging the system 2, the opinion of the majority gets more credit without any objective reason. Remember that what the majority decides is not the best choice by default!
• Overconfidence: Too often people tend to be too optimistic about their abilities. This might cause them to take bigger risks and take wrong decisions that have no objective grounds but based exclusively on their opinion. The most obvious example of this is the estimation process. It is much more often that people underestimate the time and effort they are going to spend on some problem, than overestimate.
• Availability heuristic: The information in hand is not always, or, always not all information, which we can get about a particular problem. People tend to base their decisions only with information in hand, without even trying to get more details. Too often this leads to over-simplification of the domain problem and underestimation of the essential complexity. This heuristic can also trick us when we make technological decisions and chose something that always worked without analyzing operational requirements, which might be much higher than the technology of our choice can handle.

The importance of knowing how our decision-making process works is hard to overestimate. The book's references in this section contain much more information about human behavior and different factors that can have a negative impact on our cognitive abilities. We need to remember to turn on the System 2 in order to make better decisions, which are not based on emotions and biases.