Reference Material: Universal Principles of Design 130-131

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"Designers generally have very complete and accurate system models, but often have weak interaction models - i.e. they know much about how a system works, but little about how people will interact with the system. Conversely, users of a design tend to have sparse and inaccurate system models, but through use and experience commonly attain interaction models that are more complete and accurate than those of designers. Optimal design results only when designers have an accurate and complete system model, obtain an accurate and complete interaction model, and then design a system interface that reflects an efficient merging of both models." (Lidwell et. al. 130)