But is it obvious that it ain't obvious what's obvious?
It looks as if we have a little self-referential puzzle going here. Does the Hilarian dictum apply to itself? An absence of the particular quantifier may be read as a tacit endorsement of the universal quantifier. Now if it is never obvious what is obvious, then we have self-reference and the Hilarian dictum by its own say-so is not obvious.
Is there a logical problem here? I don't think so. With no breach of logical consistency one can maintain that it is never obvious what is obvious, as long as one does not exempt one's very thesis. In this case the self-referentiality issues not in self-refutation but in self-vitiation. The Hilarian dictum is a self-weakening thesis. Over the years I have given many examples of this. (But I am now too lazy to dig them out of my vast archives.)
There is no logical problem, but there is a factual problem. Surely some propositions are obviously true. Having toked on a good cigar in its end game, when a cigar is at its most nasty and rasty, I am am feeling mighty fine long about now. My feeling of elation, just as such, taken in its phenomenological quiddity, under epoche of all transcendent positings -- this quale is obvious if anything is.
So let us modify the Hilarian dictum to bring it in line with the truth.
In philosophy, appeals to what is obvious, or self-evident, or plain to gesundes Menschenverstand, et cetera und so weiter are usually unavailing for purposes of convincing one's interlocutor.
And yet we must take some things as given and non-negotiable. Welcome to the human epistemic predicament.