"Everything," said everyone, ever.
Do I need to cite that?
Are there double standards in academic citation practices (not Standards)? Spoiler alert: most likely.
Academic citing serves important social functions, quite apart from demonstrating your 'academic rigour', and quite a bit more than a simple tip of the hat too. It's within these social functions that we can find inconsistency and dare I say hypocrisy in their use and not-use.
One of the social actions in citing is that you build collaborative consensus in the argument or idea you are developing. "See, someone else said it too."
Direct quotes are most useful when someone says an idea more succinctly or eloquently than you can be bothered paraphrasing. Undergrads are always encouraged to paraphrase as a first option (with references of course), and only direct quote when it's most useful and efficient. This makes sense, and it's also an easy way for undergrads to build essays and reports around key quotations from primary sources. And so you deploy your quotes or paraphrases, and tip your hat to the source.
One of the academic social functions in citations is the policing of the citation standard itself. This policing becomes one part in a broader systematic assessment approach. Undergrads are told time and again - doesn't matter how good your content is, if you muck up your references, you'll be failed!
But I wonder how many possible citations have been missed in unreferenced paraphrased ideas over the course of ever? At some point you're born and start to absorb ideas and thoughts through language in your family, school, society. You learn by rote and repetition, and when you have grasped an idea and can use it, twist it, poke fun at it, forget it and remember it - it's yours! And everyone else's too.
Otherwise we might as well put some meta quotes around everything we ever say, ever.
My observation about the gate-keeping function of citations is that when you've climbed the academic ladder high enough, greyed your messy hair enough, scuffed your tweed elbows enough, and held the rod to enough fresh-faced undergrads and up and coming postgrads, you're somehow allowed to start publishing books where 98% of your writing is not cited, even though 97% of it is most likely the accumulated paraphrase of a lifetime of idea-borrowing and -repurposing.
And yet I don't think there's anything wrong with this.
And contrary to what undergrads are taught, seasoned academics have no trouble dropping huge direct quote passages, sometimes a page long or more, from one of their beloved idea-parents or -partners. This is as much a show of admiration and respect as convenience. Nothing wrong with this either IMO.
Finally, how many times have you been mildly or quietly disappointed when you thought you had an original idea, only to come across someone who has already said it, and done so in a far more concise or decisive way than you had thought?
Or sometimes this might've made you feel joy and elation that you're not alone, someone else thinks and feels and sees things just like you. I hate to love it when that happens!