A scientist may realize, during a long academic career, that a widely accepted notion is not actually factual. An example for me is the fraction of adrenaline-secreting cells in human adrenal medullary chromaffin (AMC) cells. Even the authoritative textbooks for medical physiology differ regarding the fraction of adrenaline cells in human AMC cells, stating that it is 80% or 100%. This confusion may be ascribed to the substitution of the fraction of adrenaline in the catecholamines extracted from the human adrenal medulla for the fraction of adrenaline cells in human AMC cells. In this commentary, I look into the possible cause of this substitution and highlight the importance of understanding a process to reach a conclusion.