This position paper addresses the fallacies associated with the improper use of affordances in the opportunistic design of augmented reality (AR) applications. While opportunistic design leverages existing physical affordances for content placement and for creating tangible feedback in AR environments, their misuse can lead to confusion, errors, and poor user experiences. The paper emphasizes the importance of perceptible affordances and properly mapping virtual controls to appropriate physical features in AR applications by critically reflecting on four fallacies of facilitating affordances, namely, the subjectiveness of affordances, affordance imposition and reappropriation, properties and dynamicity of environments, and mimicking the real world. By highlighting these potential pitfalls and proposing a possible path forward, we aim to raise awareness and encourage more deliberate and thoughtful use of affordances in the design of AR applications.