This reflective paper attempts to explore how clinicians working in an increasingly complex, data-driven world of healthcare provision, interpret, analyse, assimilate, and disseminate commonly encountered numerical data. It is suggested that on occasion during this process, unintentional errors of clinical reasoning and critical thinking may occur. The main theme explored is how we as clinical neuropsychologists, as part of clinical reasoning, communicate and process information, more specifically numbers, in our own minds, as a currency for conveying our ideas, findings, apprehension, frustrations, or achievements in our respective worlds of daily clinical work. Practical, practice-based examples are used to reflect on, and ask questions about some of these hypothetical errors that could potentially occur. The examples of errors of clinical reasoning and critical thinking explored in the paper include the following. A failure to critically question the objectivity of data. A tendency to default to complexity when communicating data or clinical findings, when parsimony could potentially provide a more transparent explanation. A ‘blindness’ to situations where an absence of evidence for an argument may exist. A failure to consider alternative hypotheses which could provide a better explanation of the phenomena under consideration. Practical, psychologically informed strategies to avoid or minimise these errors are suggested. It is hoped that the paper will stimulate further reflection and questioning about a potentially ‘hidden’ aspect of our role as scientist-practitioners working in complex, busy, and at times overwhelming, healthcare environments.