The combination of what we have explored and what we have still to evaluate actually comprises our environment, insofar as its nature can be broadly specified-and it is to that environment that our physiological structure has become matched. One set of the systems that comprise our brain and mi nd governs activity, when we are guided by our plans-when we are in the domain of the known. Another appears to operate when we face something unexpected-when we have entered the realm of the unknown.
