The source, an excerpt from CAP 737 Chapter 7 - Surprise and Startle, discusses the difference between the startle reflex and the fight or flight response, particularly in the context of pilot performance and aviation safety. The startle reflex is presented as a momentary disruption with little lasting impact on cognition, while the fight or flight response, triggered by a perception of serious threat, results in a sustained, highly-focused, and potentially detrimental narrowing of cognitive function. The text explores how the fight or flight state can create a vicious circle for pilots when dealing with ambiguous or complex problems on modern flight decks, favoring simple, well-learned tasks over complex assessment. Finally, the chapter suggests training resolutions and countermeasures, such as using simple, rule-based tasks (like checklists) to interrupt the negative cycle and build pilot confidence against unexpected events.