This article cautions against the naïve use of predictive techniques by homelessness service providers. Prediction is hard and may be impossible. Prediction does not automatically lead to socially optimal assignments. On the other hand, mechanism design, which does not rely on top‐down predictions, can be used to good effect. Moreover, fairness counts as well as optimality—and may be easier to achieve. I use examples from fire service, central banking, police patrol, tax auditing, art, finance, soup kitchens and cadaveric organ allocation.