“Let's say we're a golf company and you say there's 50 million golfers in the US, that's our TAM. You'll find pretty quickly that there aren't 50 million golfers who play golf on a frequent basis, maybe 20 million. You're omitting a key factor which is commitment.”

Commitment is the variable founders forget — 50M golfers ≠ 50M subscribers

For subscription products the gating variable isn't whether someone fits the category — it's how committed they are. Surfline doesn't care how many people have surfed once; it cares how many surf often enough to pay. Cut your TAM by commitment frequency before you model anything.