An agent operating in an unpredictable world must be able to take advantage of opportunities but cannot afford to perform a detailed analysis of the effects of every nuance of the current situation on its goals if it is to respond in a timely manner. This paper describes a filtering mechanism that enables the effective recognition of opportunities. The mechanism is based on a characterization of the world in terms of reference features, features that are both cheap and functional and that appear to be prevalent in everyday life. Its use enables the plan execution system PARETO to recognize types of opportunities that other systems cannot. Reference features can also play a role in the detection of threats, and may be involved in the development of expertise.