Things-plus-me is the only knowable, and consequently the only 'ignorable.'
The law of ignorance hence is that 'we can be ignorant only of what can be known,' or 'the knowable is alone the ignorable.'
1610s, "not to know, to be ignorant of," from French ignorer "be unaware of," from Latin ignorare "not to know, disregard" (see ignorant). Sense of "pay no attention to" first recorded 1801 (Barnhart says "probably a dictionary word"), and not common until c.1850. Related: Ignored; ignoring.