Teaching #57: The Buddha's Fire Sermon
The Buddha characterized every aspect of your experience in daily life as “burning.” The Buddha wanted you to feel this burning in your life with all its difficulty, uncertainty, and stress and for you to realize that this burning is inherent and impersonal and that it applies to pleasant and unpleasant phenomena alike.
Chapter 15, Pg 177-178
For your reflection: Observe as objectively as you can the phenomenon of your mind registering something. Are you able to notice that there is a degree of stress or friction just in making the effort? This is what the Buddha meant by burning.