&gt;<i>Facts beat theory.</i><p>Not necessarily. Facts (in the sense of &quot;anecdata&quot;) are simple observations.<p>The only make any sense against or in favor of something when we combine them with a theory why it is so.<p>OK, students faring better on exams when they are taught with tau is an argument in favor of tau only if we theorize (assume) that it was the tau&#x2F;pi thing that made the difference.<p>Whereas it could just be that the second group of students was just better naturally (e.g. a good school vs a mediocre one), or just a chance outcome, due to the small sample we picked, or the teacher going for tau was also better at explaining and would have fared just as good if he also was the one to teach the pi group.