The powers of human genetics and genetic technologies have transformed the complexities of neurology and neuroscience at the basic, translational, and now also the clinical level. We have left an era of black and white views of causative genetic variation and are entering a period of more than 50 shades of grey, fascinated with DNA variants that increase or decrease risk, epigenetic modification, and an unexpectedly large number of variants of unknown or potentially pathogenic significance. Loss-of-function alleles and even complete human gene knockouts for certain genes appear to be compatible with a normal phenotype.