We present a critical discussion of research into the nature of design expertise, in particular evaluating claims that opportunism is a major influence on the behaviour of expert designers. We argue that the notion of opportunism has been under-constrained, and as a consequence the existence of opportunism in expert design has been exaggerated. Much of what has been described as opportunistic design behaviour appears to reflect a mix of breadth-first and depth-first modes of solution development. Whilst acknowledging that opportunities can arise in the design process (e.g. serendipitous solution discovery), such events might equally confirm structured behaviour as cause unstructured behaviour. We argue that the default mode for truly expert designers is typically a top-clown and breadth-first approach, since longer-term considerations of cost-effectiveness are more important for expert designers than short-term considerations of cognitive cost. However, there are situations (e.g. when faced with a highly unfamiliar design task) where it is cost-effective for experts to pursue a depth-first mode of solution development. The implications of our analysis for the development of methods and tools to support the design process are also discussed.