In my opinion, empirical evidence in the form of observation, experience, or experiment should be used in almost all areas of knowledge in order for progress to be made. But, however well it may have been confirmed by careful tests, the possibility can never be precluded that it will may have to be discarded later in the light of new and disconfirming evidence. Thus, all the theories and hypotheses of empirical science share the provisional character of being established and accepted "until further notice" [ 12 ] . After all, certainty cannot be found in any area of knowledge and discoveries and findings proved by experiment or observation may turn out to be false after some years. Observation, in particular, can be influenced by expectation, advances in technology, as well as psychological factors. Thus, every scientist should question and analyse any findings in the most objective way and not allow prejudice influence his thoughts and his results. As we saw, even "mathematical certainty" has been questioned. And as Einstein said: "The important thing is not to stop questioning" [ 13 ] .