The emotional system of the brain is one of the most powerful learning systems that we have, but it is an implicit learning system. It can contribute to explicit memory, so that we have memories about emotional situations that are explicit and consciously available. But the many systems involved in implicit learning are what give rise to physiological and other responses in the presence of stimuli associated with past pleasure or danger. Nature and nurture. We come into the world capable of being afraid and capable of being happy, but we must learn which things make us afraid and which make us happy.
Fear is the emotion most responsible for reinvigorating the study of emotion.
The amygdala is programmed to react without benefit of input from the thinking part of the brain, the cortex. Eventually the cortex gets involved, but this processing takes longer. We also know that the amygdala's input to the cortex is much stronger than communication the other way. An emotional reaction like fear can more easily gain control over the cortex and influence cortical processes than the cortex can gain control over the amygdala. This may explain why psychotherapy is such a difficult process.