Cognitive biases affect decision making in systems engineering (SE). Daniel Kahneman, 2002 Nobel laureate for his pioneering studies of cognitive biases in economic decision making, describes many disparate cognitive biases as abstractly belonging to one higher-level bias, that of attribute substitution. Attribute substitution occurs when an answer about a target attribute is unconscientiously provided by referring to a sublevel heuristic attribute that is simpler or more easily accessible, while other subattributes are ignored. The essence of this biasing process is generalized with real examples at all phases of the systems engineering process. Willful awareness of attribute substitution, however, can help prevent erroneous reduction in focus, and ensure that valid systems are being built to satisfy customer needs.