The article advises software engineers to "do the simplest thing that could possibly work" when designing, fixing, maintaining, or architecting systems. Instead of aiming for ideal but complex solutions, engineers should deeply understand their current systems and implement the simplest effective solution. Simple design often appears underwhelming but is a hallmark of mastery, akin to a martial arts master’s minimal, decisive movements. Examples include the Unicorn web server, which relies on simple Unix primitives, and Rails REST APIs, which provide straightforward CRUD functionality with minimal complexity. The author illustrates this with the example of adding rate limiting to a Golang app: rather than immediately adding Redis and complex infrastructure, start with simpler in-memory counting or leverage existing features like rate limiting in the edge proxy. The author acknowledges three common criticisms of this approach: 1. It can lead to inflexible "big ball of mud" codebases. However, hacks are actually not simple—they add hidden complexity and are easier to conceive but harder to maintain. True simplicity requires deep understanding and careful engineering to find the genuinely simplest effective solution. 2. "Simplicity" can be subjective. The author defines simple systems as having fewer components to manage and fewer internal dependencies, promoting stability. For example, in-memory rate limiting is simpler than Redis because it requires less operational overhead, even if Redis may seem simpler functionally. 3. Concerns about scalability often discourage simple solutions. The author argues that prioritizing massive scale prematurely leads to over-engineering and inflexible designs. Systems should first work well at their current scale, adapting progressively when actual scale requirements arise. Over-anticipating scale causes unnecessary complexity and coordination overhead. In conclusion, the author emphasizes that most design is done poorly because engineers lack a complete understanding of their systems. There are two approaches to software design: predicting future requirements and building for them, or designing the best system for current needs by doing the simplest thing that could possibly work. The author advocates strongly for the latter as a practical, effective engineering principle that embraces YAGNI ("You Aren’t Gonna Need It") above all else.