Average AI product gross margin is 52% against the 80% that defined SaaS, and inference eats about 23% of revenue. Every growth instinct you inherited was formed in a world where your best user cost you nothing.
There's a rule most of us absorbed without ever being taught it: engagement is free. One more session, one more entry, one more day in the app pure margin. That rule is why "north star metric" articles exist, why every dashboard puts DAU at the top, why nobody ever asked you what your heaviest cohort costs. It held for twenty years because the marginal cost of serving a software user really was approximately zero.