Why does wood siding cup, and how do you actually stop it?

Had siding cup on me once and went down a rabbit hole figuring out why. The short version surprised me: if the wood was dried properly, cupping is mostly an install problem, not a species problem. The big causes are no ventilation behind the boards and moisture getting into the backs and ends. So get it on furring with an air gap, give the backs a thin seal, and don't nail boards up bone dry and jammed tight. Do that and the species barely matters. Mine came back primed from a specialty hardwood supplier which saved me coating the backs on site.