Do we need a sophisticated theory to describe "herd behavior"? And does it really challenge the "efficient markets" theory? I would say that an individual is ma

Do we need a sophisticated theory to describe "herd behavior"? And does it really challenge the "efficient markets" theory? I would say that an individual is making a _rational_ decision even if it is based on the behavior of others. I see that as valuable information before making a decision. If I understood it correctly, the author sees it as irrational.