Most documentation fails because it serves the author's organizational instincts instead of the reader's task-completion needs — the information architecture, writing patterns, and testing methods that produce genuinely useful developer documentation.

Technical documentation is one of the highest-leverage investments a software product can make, and one of the most systematically underinvested. The gap between a product that developers adopt enthusiastically and one that they abandon after a frustrating first hour is often not the product itself — it is the documentation. The first experience a developer has with your product is almost certainly your documentation, and that experience sets the emotional frame for every subsequent interaction.
The most common failure in technical documentation is optimizing for completeness at the expense of accessibility. Comprehensive API references, exhaustive configuration options, and detailed architecture diagrams are valuable — but they are the wrong starting point for a developer encountering your product for the first time. The optimal documentation architecture begins with a getting-started path that takes a developer from zero to their first working integration in under thirty minutes, and only then provides the comprehensive reference material that supports production use.
Diátaxis — the documentation framework developed by Daniele Procida — provides the most practically useful mental model for documentation architecture. The framework distinguishes four documentation types: tutorials (learning-oriented, practical step-by-step), how-to guides (task-oriented, solving specific problems), reference (information-oriented, comprehensive), and explanation (understanding-oriented, conceptual). Most documentation projects conflate these types — writing reference material in tutorial format or tutorial content buried in reference pages — creating documentation that serves none of its purposes well.
Code examples are the single highest-impact element in developer documentation. An accurate, runnable code example in the reader's preferred language communicates more than three paragraphs of prose. The critical investment is ensuring that code examples remain accurate as the product evolves — broken examples in documentation create more support friction than no examples at all. Documentation pipelines that automatically test code examples against the actual product on every release are increasingly standard practice among developer-experience-focused companies.