Humans unconsciously substitute a complex, difficult judgment with an easier one. When asked to solve a difficult problem or answer a complex question, humans often substitute it with an easier one and attempt to solve/answer that one, and then use that for decision-making.
It is a fundamental heuristic that is triggered when the difficulty of analysis increases. Effectively, Attribute Substitution simplifies decision-making, problem-solving, and judgments/evaluations by a great deal. However, sometimes, the substitution is inappropriate to the decision and that leads to improper analysis.