Naive readers think that Hal gets hit on the head a lot just because
(a) the Universe itself hates him;
(b) the writers think it's hilarious;
(c) Hal himself is an idiot.
All those are true, of course. But you and I are wise enough to realize that there's a deeper literary purpose to it all. We understand that the leitmotif of Hal getting hit on the head is a metaphor.
Hal Head Hitting (H3) is political allegory of the subtlest order, which is why we give it such respect here at the Absorbascon.
Hal Jordan personifies the post WWII man. Former military man in the glamorous 1950/60s career of test pilot. Wears a suit and tie to baseball games, which he finds so exciting he loses track of time. A sexist pig, but only out of ignorance, not ill will. A company man in love with his employer (cleverly personified as the beautiful Carol Ferris). Confident in his own abilities and the power of the democratic arsenal at his (literal) fingers. Hal Jordan WAS his time.
What is his weakness? Yes -- the YELLOW PERIL itself: communism, which threatens to undo our post-war prosperity by undermining the concept of individual superiority (which the vain, smug Hal evokes incredibly well). Along with his fellow pseudomilitary peacekeeper colleagues from similar but distant societies, Hal is directed by the distant Guardians, who with their light blue and white visages clearly are meant to embody the United Nations, ordering local forces to squelch possible political instabilities or challenges to their universal authority.
The "H3 Phenomenon" is a warning to us all. We the post-war Western World (as represented by Hal Jordan) must remain ever vigilant against sneak attacks. One "klonk" to our metaphorical heads (our "heads of state", as it were) and our society can be rendered senseless, our all-powerful arsenal of democracy dangling uselessly from our unconscious hands. We must remain alert so that our leaders are not blindsided by ideological ambush, which is why the search for communist sympathizers within the ranks of our political and cultural elite is so important, lest we be nurturing a Sinestro/Castro in our very bosom.
It's either that, or Hal just gets hit on the head a lot.