Ok, so none of these realizations has actually ruined science fiction for me, but they are pretty funny nevertheless.
#4. Sci-fi Needs a Straight Man Like a Laurel and Hardy Routine
The bulk of the workload in writing science fiction/fantasy is creating your whole world from scratch. It's a hell of a lot of fun, but it also has some unique problems. Characters, by being from this world you've just hand-built, are naturally going to be referring to places and objects and sometimes even speaking in a language that is completely foreign to the reader. To deal with this issue as a writer, you can fill the narrative with clunky exposition, rabidly notate the entire thing and hope your readers like cross-referencing as much as they like space battles (not always a losing bet), or you can attempt to skillfully weave information and plot by virtue of your many practiced years in fiction.
Or you could take the other option: Chuck a dumbass into your story who literally doesn't understand a thing, thus forcing all of the other characters to constantly stop and explain every aspect of the world to him. Like so:
"General Klogg's Pogofighters are bouncing over the city walls! Quick, to the rhythm-cannons!" N-dah Gaim, robo-temptress of the Seventh Veil, screamed in alarm.
"General who's whatfighters are doing huh now?" Biff Manface asked (manfully).
"I forget, Manface, despite your chiseled jawline and just ... really, truly rockin' pecs (seriously, they're so, so good) ... that you are but a human, and a stranger to our lands. General Krogg is the former leader of Klogglandia's dancing warrior caste, you see, and his elite band, or 'crew,' of Krumping assassins have ..."
And so forth.
If you think that's a hack move that you, as a discerning reader, wouldn't tolerate, think again. It's been utilized in nearly every famous sci-fi work in history.