This is a cute quip from Seth showing how we collectively agree on shared perceptions like the weather, etc. and then that agreement is fed back to us in our personal 3D experience as the primary sense data we manifest. Being aware of this primary sense data “closes the loop” of manifestation and the illusion ticks along just fine.
The 3D illusion’s "wheels come off" when our logical thought processes or other distractions get in the way of our awareness of primary sense data! That’s like the ancient Greek philosopher that got run over by a chariot because he ignored his primary sense data and had convinced himself logically that the chariot didn’t exist.
“You form your own reality. Yet if you are in the Northeast in the wintertime, you had better be experiencing a physical winter, or you are far divorced from primary sense data.”
(The Individual and the Nature of Mass Events, Session 812)