The notion of consensus has recently taken on great importance in science although its relevance as a judge of the validity of scientific theories is poorly founded. The same applies to simulations of complex processes to which a demonstrative power is attributed. Studying why theories that have now been abandoned were nevertheless accepted for very long periods of time is instructive in this respect. Three examples are particularly demonstrative: the theory of the four elements constituting matter proposed by Empedocles, and then modified by Aristotle, the geocentric world system to which Ptolemy gave its paradigmatic form, and the question of the age of the Earth, which appeared to have at last found a rigorous solution at the end of 19th century. The first two examples deal with theories designed in Antiquity that remained unchallenged for more than one millennium - two, in fact, for the former - despite observational evidence that contradicted their foundations. A great explanatory power and, for the Ptolemaic system, the ability to calculate astral movements precisely relegated these contradictions to the background. The age of the Earth, on the other hand, was not unanimously agreed upon when four entirely independent methods designed by physicists yielded values ranging from 26 to 100 million years. The credibility of these rigorous approaches gave rise to a consensus before the term was in common usage, in that many naturalists remained convinced of much longer periods. Now, these were eventually proven when the discovery of radioactivity led to the development of true geological chronometers. Of course, the conclusion is that neither unanimity, let alone consensus, nor the conformity of a model with observations constitute criteria for truth. At the root of long-admitted erroneous thesis are methodological flaws and cognitive biases. More than a century ago, geologist T.C. Chamberlin analyzed them particularly well in his theory of multiple hypotheses, which requires, among other things, that no type of explanation be favored a priori. The only way to approach truth is through free, open debate and the questioning of groupthink, the intervention of newcomers to the field being highly desirable from this point of view. Since its beginnings in Greece more than 25 centuries ago, it is indeed through countless controversies that science has gained its solid foundations and ensured its development to the present day.