The boundaries of reason are often self-imposed limitations and are often subconscious.
What is the boundary of reason?
To be reasonable and practical within the bounds of currently reasonable limitations. These boundaries are movable. These boundaries are changeable.
Both so we don’t take ourselves too seriously, and to confuse matters a little, consider that it will also be true that if we do expand the limitations of current perceptions, we continue to be bound by expanded limitations. This new boundary is useful yet has its limitations. Things like this will occur at the edge of reason.