Existence.

"If no one turned round when we entered, answered when we spoke, or minded what we did, but if every person 'cut us dead', and acted as if we were nonexisting things, a kind of rage and impotent despair would ere long well up in us, from which the cruellest bodily tortures would be a relief; for these [tortures] would make us feel that, however bad might be our plight, we had not sunk to such a depth as to be unworthy of attention at all." - William James, 1890 I am unworthy