You could interpret your question outside of the context of mathematical proof. It seems like your question was phrased broadly-enough to allow this interpretation.
There are what are perhaps the most subjective aspects of mathematical reasoning:
1) What questions do we consider important?
2) What results do we consider worthy of publication?
3) What do we consider worthy of teaching our students?
I suppose this is a type of metamathematical reasoning. But arguments from authority frequently get used in these situations.
Especially in grad school I seemed to encounter far too many people with fantastical images of certain mathematicians, frequently fields-medalists, sometimes with little understanding of what these people have accomplished. The further I get from grad school the less of this I see, thankfully.