The modern concept of DevSecOps combines the principles of DevOps (improving quality and, above all, speeding up delivery) with application security. But does this also work in practice? In this talk we share our many years of experience from a large, highly agile project. We show our successes, but also our mistakes in the area of DevSecOps. These lessons learned help those responsible to recognize problems early and to prevent them with the help of best practices.