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.