Chapter 5. Postel’s Law

Be conservative in what you do, be liberal in what you accept from others.


Designing good user experiences means designing good human experiences. People don’t behave like machines: we are sometimes inconsistent, frequently distracted, occasionally error-prone, and usually driven by emotion. We expect the products and services we interact with to intuitively understand us and be forgiving. We expect to feel in control at all times, and we’re generally annoyed when asked to provide more information than is necessary. At the same time, the devices and software we use vary greatly in terms of feature support, capabilities, and form factors. To be capable of meeting users’ expectations, the products and services designers build must be robust and adaptable. Postel’s law, also known as the robustness principle, gives us a guiding ...

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