Long-term
Your child used to run to you. Somewhere in the last few years, that changed. They're guarded now, repeating grievances that don't sound like theirs, distant in ways you can't trace to anything specific. There was no single incident. Just a slow accumulation of small shifts, none of them alarming enough to act on.
By the time it's visible, it's already done.
The game
One parent has more daily access to the child. That access is also access to the child's developing understanding of the other parent. Small interventions (a comment here, a reframing there, an absence explained in a particular way) compound over time. Each is deniable in isolation. The cumulative effect is a child whose perception of you has been shaped by someone with an interest in shaping it.
The strategy doesn't require malice. It can run on hurt feelings, self-justification, and the natural tendency to process a failing relationship out loud in front of the people closest to you.
The equilibrium
There's no single incident to point to. The child believes their perceptions are their own, and in a sense they are, which is what makes this hard to challenge. Confronting it directly tends to backfire: the child experiences it as pressure, and the alienating parent can point to the confrontation as evidence.
Dominated strategies
Responding to the child's distance with frustration or withdrawal is the dominated strategy. It confirms the narrative being built and accelerates the process.
The only move that doesn't lose ground is consistent, patient presence. Not pressing the child to take sides, not escalating with the other parent, not making the child a messenger for the adult conflict. The relationship has to be rebuilt directly. It's slow and it's unfair. It's also the only approach that works.