Hippocrates Praeceptiones 2

[2] But conclusions which are merely verbal cannot bear fruit, only those do which are based on demonstrated fact. For affirmation and talk are deceptive and treacherous. Wherefore one must hold fast to facts in generalisations also, ¹ and occupy oneself with facts persistently, if one is to acquire that ready and infallible habit which we call the art of medicine. For so to do will bestow a very great advantage upon sick folk and medical practitioners. Do not hesitate to inquire of laymen, if thereby there seems likely to result any improvement in treatment. For so I think the whole art has been set forth, by observing some part of the final end in each of many particulars, and then combining all into a single whole. So one must pay attention to generalities in incidents, with help and quietness rather than with professions and the excuses that accompany ill-success.