Observation: The one who is incompetent at rational argument will never be persuaded of his incompetence by rational argument; nor will he be persuaded rationally of his position’s irrationality.
Update: corrections made at comments 2 and 3.
Corollary 1: If I am rationally incompetent I may irrationally persist in thinking that I am competent. (See also the Dunning-Kruger Effect.)
Corollary 2: If I believe I am rationally competent it is no sure sign that I am.
Corollary 3: If I believe my arguments are rational it is …