The world has been startled by the irresponsible experiment of He Jiankui, who used CRISPR to genetically modify human embryos. In this viewpoint, we explore the phenomenon of moral luck in medicine and its bearing on the limits of simple judgements of the kind “everything that ends well is well” or “someone broke the rules, and is therefore blameworthy”. The risks involved in scientific and medical experiments are often brushed aside, when they turn out well. The clinical application of CRISPR in the human germline is presently too risky to be used without more preclinical research and unacceptable without broader societal support, which justifies the call for a moratorium by the scientific community. However, such policies do not determine how to assess cases, where someone was willing to take such risks beyond all rules, guidelines and regulation and succeeds. The policies including the proposed moratorium are as unanimous about the undesirability of current applications of clinical germline editing as they are about the potential importance of this research. What if this potential is achieved by breaking the rules? The paradox of moral luck impinges on this debate. In our analysis, we rebut simplified judgments and advocate a more balanced view on the relation between moral responsibility and the societal consequences of medicine.