History can be divided in pre-classicism, classicism, modernism, and postmodernism. Pre-classicism is a collection of knowledge accumulated over hundreds of thousands of years until Greece, classicism over few thousand years since Greece, modernism over a century or so since 18th century, and postmodernism over few decades in the second half of 20th century. Classicism, modernism, and postmodernism removed some knowledge from previous periods, causing a drastic contemporary reduction in knowledge and increase in risk and values.
Metamodernism, coming after postmodernism, aims to restore the lost knowledge from each period making it available for contemporary use. This is enriching knowledge from each of the periods making it safer and more valuable. Modernism and postmodernism especially had little time to develop knowledge yet have great power and are therefore very unsafe. Their risks and quality would be lowered by adding pre-classical and classical knowledge.