"One important detail is that actions that have not yet been tried in a state s are always assumed to lead immediately to the goal with the least possible cost, namely h(s). This optimism under uncertainty encourages the agent to explore new, possibly promising paths.
Artificial Intelligence, A Modern Approach (Russell & Norwig)
Amusing what theory can teach you about how to lead life, and explain its inevitable disappointments. Of course, literature got there first with ""