Certificates of incapacity for work are considered a central piece of evidence in labour law. A recent ruling by the Düsseldorf Regional Labour Court, however, demonstrates that if the evidential value of such a certificate is undermined, the certificate alone is no longer sufficient—even if the treating physician testifies in court. This is particularly relevant in the context of dismissals, where the requirements for full proof of incapacity for work are becoming increasingly precise. This article outlines what courts focus on, highlights common weaknesses, and explains the practical significance of a physician’s testimony.