[Title] Every cloud has a silver lining and what we can learn from it [Full name] Jakub Jermář [Short bio] Jakub is a long-time developer of the HelenOS operating system and one of the project founders. Jakub helped to design and develop various parts of the system, including its kernel and the file system layer. [Estimated duration] 30m [Abstract] During the development of HelenOS, we have made a couple of wrong technical decisions that required a major fix later on. In this talk, I will mention several instances of these mistakes and describe how we fixed them. I will also attempt to generalize the cause of each problem and give some bold recommendations for avoiding it. The idea is to share this part of our experience with the other projects so that we can learn from each other.