Uttering such a common phrase as a preamble of an opinion, informed or not, displays the opposite of what is supposedly meant to express: a total lack of humility.
And a certain absence of awareness, too? Yes, maybe. Perhaps.
Labeling yourself as something does not make you a representative of such a label. Words can be tricky, my friend.
Therefore, the principle would be like this:
The assertion of *any given quality or positive trait* proves its inexistence in the utterer.