That economic agents can achieve efficient outcomes which are not part of their intention was the key principle articulated by Adam Smith, but few outside of the Austrian and Chicago traditions believed it, circa 1956. Certainly I was not primed to believe it, having been raised by a socialist mother, and further handicapped (in this regard) by a Harvard education, but my experimental subjects revealed to me the error in my thinking (emphasis added)
Economists do NOT think that people analyse every decision they make in a pile of analytical detail. However, economists do believe that the actions that people act within their “interests” – and that this process can be described using mathmatics. Maths provides a language to describe action – the agents themselves do not need to be able to do the maths.