Importance of Internal Coherence and External Validity in Evaluating Ideas

The key focus is on evaluating ideas based on whether they are internally coherent and externally valid. It is noted that people tend to test ideas for external validity only when they are internally coherent. The speaker emphasizes the significance of selecting foundational books that serve as good starter pieces, even if previous books were not well-received. They suggest revisiting past readings to identify gaps and choose further books for exploration, highlighting the importance of building upon existing knowledge.