Both the yield and rate of star formation can vary considerably in clouds, independent of their mass and size, but above a certain threshold in column density clouds become predictable. In this paper we find that the star formation rate is proportional to the cloud mass above an extinction threshold of A_K ≈ 0.8 mag, corresponding to a gas surface density threshold of Σ_gas ≈ 116M_⊙ pc². (or volume densities about 10⁴ cm^-3). In other words, once you have dense gas you have stars. The more dense gas you have, the more the stars you'll produce. Understanding star formation is understanding how nature transforms diffuse gas into dense gas. Easy.