"Later, I realized that the mission had to end in a let-down because the real barrier wasn't in the sky but in our knowledge and experience of supersonic flight"

This quote by Chuck Yeager is describing the objective of breaking the sound barrier. Initially, the objective was believed to be a physical barrier in the sky, however Yeager later on recognized that the genuine barrier was the lack of understanding and experience of supersonic flight. This awareness suggested that the mission was doomed to end in a let-down, as the barrier was not something that might be broken through physical means. Yeager's quote is a tip that knowledge and experience are often the most essential factors in attaining success. It also acts as a pointer that even when confronted with seemingly overwhelming barriers, it is necessary to remain open to the possibility that the genuine barrier might be something that can be gotten rid of through knowing and experience.