And did I say or even imply it was? Height is comparably heritable to adult IQ (and coincidentally is even strongly correlated with such) at around 0.8, but obviously somebody who is e.g. malnourished as a child will never reach their height (or intelligence) potential. And that's precisely why heritability is useful. It lets you create a ballpark estimate for the overall average influence of genetic vs contemporary environmental factors. So genetic factors would tend to explain about 80% of the differences in heights, with environmental factors taking up the remaining 20%. The heritability for factors without a genetic component is zero.