Every design problem has an essence, a core set of considerations that must be understood and “nailed” in the design solution for it to solve the problem successfully.

This essence can be disruptive: changes in the core drastically alter the peripheral decisions that need to be made. Experts focus their efforts on the essence first, and delay expending effort designing on the periphery.

Experts imagine how a design will work — simulating aspects of the envisioned software and how the different parts of the design support a variety of scenarios.

When working with others, experts regularly walk through a design by verbalizing its operation step-by-step. When alone, they simulate mentally, exercising the design repeatedly over time.

In the same way that architects walk cities to examine and take inspiration from existing buildings, software experts examine the designs of other software to “see how they did it.”

They frequently do so in response to a particular challenge they face, but they often also spend time looking around just to add to their repertoire of possible design solutions to draw upon in the future.

Experts often step back from the stated problem and consider the problem space more broadly, looking for alternative ways of understanding “what the problem is.”

They may change direction by reconceiving the problem space, or by addressing a different problem in the same space. They intentionally choose somewhat different goals from the original design problem, as this leads to insights either into where the real problem lies, or into how to overcome key obstacles.

Design regularly involves error: things that “go amiss,” misunderstandings, obstacles, wrong turns, emergent issues. Rather than fearing error, experts embrace error as opportunity.

They accept it as an inherent part of design and take time to explore both the failure and the context around it. Understanding what happened often reveals insights about the problem — or about the solution — such as assumptions, misconceptions, misalignments, and emergent properties.

While it is natural to focus on what a design must accomplish, experts also spend time thinking about what a design is not intended to do.

In articulating and considering boundaries, they discover where they are over- and under-designing.