Civilization can be thought of as layers upon layers of decisions. When we make a decision, we take into account a host of different factors, depending on the nature of the individual decision. The final decision, if made well, is in a sense a summary and a distilling of all the factors that were considered in the making of the decision. When we make a decision that can be considered as "built upon" previous decisions, then the later decision, if done well, can be considered to be a distillation of previous decisions as well as new information.
In today's culture, it is not uncommon to discard old decisions, in essence to discard the distillation process performed by earlier generations of deciders. But unless we have somehow rigorously taken into account all of the factors and information and experience that earlier deciders pulled together to make their decisions, our fresh decisions will carry a significant amount of ignorance, and thus be weaker decisions.