S-curve

The shape technology and category adoption usually follows: slow at first, then rapid, then flattening as the market saturates.

The practical difficulty is knowing where on the curve you are, since the early part of an exponential and the early part of a failure look identical for several years.

The forecasting error the curve exists to prevent is extrapolating the steep middle section forever. Growth decelerates, and the deceleration usually begins earlier than the consensus expects because the easy customers were acquired first.

Penetration data is the best available position-finder.