Tutoring became a marginal-cost-zero product

Personalized one-to-one tutoring produced the best outcomes and the worst economics — it didn't scale. AI tutors changed the cost curve: the marginal cost of an additional learner approaches zero.

The scarce resources are now curriculum quality, trust, and the relationship — not tutor hours.

Signal: when the expensive part of a service hits zero marginal cost, the moat moves to brand, outcomes, and distribution.