What we can also learn is that almost no class of reactions is inherently meant to be either concerted or stepwise; they only happen to exhibit one mechanism or another for most of the cases we have encountered. The prevailing beliefs regarding which class of reactions corresponds to which mechanism are typically based on the most commonly encountered examples. The collection of these examples often has led to a statistical, but not directly causal, association with a particular mechanism. This predominant belief that a certain class of reactions must follow a specific mechanism may illustrate another origin-survivorship bias.