Why is writing important? Mainly, out of egotism, I suppose. Because I want to be that persona, a writer, and not because there is something I must say. Yet why not that too? With a little ego-building — such as the fait accompli this journal provides — I shall win through to the confidence that I (I) have something to say, that should be said.
My “I” is puny, cautious, too sane. Good writers are roaring egotists, even to the point of fatuity. Sane men, critics, correct them — but their sanity is parasitic on the creative fatuity of genius. (link)
The "creative fatuity of genius"; I think she might be thinking of Norman Mailer. Here one can't help but think Sontag is criticizing the discourse of "genius" even as she's aspiring to join the club. I also find it intriguing that Sontag writes about discovering and reading the diary of her friend (and lover, I believe), Harriet Sohmers -- where she's found a very unflattering
Confessions, I mean sincere confessions of course, can be more shallow than actions. I am thinking now of what I read today (when I went up to 122 Bd. St-G to check for her mail) in H’s journal about me — that curt, unfair, uncharitable assessment of me which concludes by her saying that she really doesn’t like me but my passion for her is acceptable and opportune. God knows it hurts, and I feel indignant and humiliated. We rarely do know what people think of us (or, rather, think they think of us).. . .Do I feel guilty about reading what was not intended for my eyes? No. One of the main (social) functions of a journal or diary is precisely to be read furtively by other people, the people (like parents + lovers) about whom one has been cruelly honest only in the journal. Will H. ever read this? (link)
In short, no "confession" is ever sincere. And diaries are always meant for other eyes: either to be discovered by the subjects under discussion, or (since the diarist presumes she will be famous, and in this case she will be) the general public. Anonymous blogging is somewhat similar, I think: one unconsciously wants to be found out.