Siegel opens by defining the mind not as a static thing located solely inside the skull, but as an emergent process — the regulation of energy and information flow — that arises from both neural activity and interpersonal relationships simultaneously.

Why this dual framing matters:

• Traditional views treat the brain as a self-contained organ and relationships as merely something the brain "does"; Siegel argues relationships literally shape the brain's structure, especially early in life
• This is the founding premise of the field he calls interpersonal neurobiology — the mind, brain, and relationships are three facets of one reality, not three separate systems
• It reframes psychological development as inseparable from social experience, giving a biological basis to ideas long held informally in psychotherapy

This integrative premise underlies every subsequent chapter's argument that healthy development requires both a functioning brain and healthy relational experience — neither alone is sufficient.