Do you need to build a State Machine at least once in your career?

State machines are a pattern most developers encounter without recognizing them. When a simple status field grows into a web of transition rules, guards, and race conditions, you're already dealing with a state machine. The post explains common pitfalls of ad-hoc implementations — invalid transitions, missing guards, scattered business logic, and race conditions — and shows how a proper state machine model makes systems explicit, constrained, and predictable. A full Ruby implementation is provided, including a builder DSL and two working examples: a traffic light and an order workflow with guards.