Companies often combine agile and plan-based methods to so-called hybrid development approaches to benefit from the advantages of both. Recent research highlights conflicts introduced when combining agile and plan-based approaches in the different phases of the software lifecycle. For example, using both agile and plan-based methods during the requirements engineering of a project requires a decision on how many requirements should be gathered up-front and how many can be gathered during the runtime of a project. These conflicts need to be solved in order to construct a successful development approach. In order to investigate why the conflicts exist, how they are addressed in industry, and how they are related to each other, we performed a multi-case interview study with 15 practitioners. Our results reveal that the conflicts exist because companies use plan-based approaches to structure their agile development and define spaces of freedom and flexibility at the same time. From this insight and our results, we derive a theory that shows how companies structure their development stepwise by defining frames.