Architectural mismatch stems from mismatched assumptions a reusable part makes about the system structure it is to be part of. These assumptions often conflict with the assumptions of other parts and are almost always implicit, making them extremely difficult to analyze before building the system. To illustrate how the perspective of architectural mismatch can clarify our understanding of component integration problems, we describe our experience of building a family of software design environments from existing parts. On the basis of our experience, we show how an analysis of architectural mismatch exposes some fundamental, thorny problems for software composition and suggests some possible research avenues needed to solve them.