Having your memory trick you and you then borrowing a turn of phrase, non obvious line of logic (especially without confirming it yourself or attributing it) or something similar can be a serious thing. Academics and research often have this as a worry. Handle it properly (which in many cases includes having your new paper/book/report/... run through a computerised check not unlike those used on students beforehand, not to mention it is one of the reasons many academics/researchers/similar are strongly encouraged to keep dated notebooks and journals) and we can probably carry on with life. Related is a favourite thing for me to see is when a new popular film, TV show or something uses an unpopular word and then notice the amount of people working it in there like it was on their word calendar or something; around the time Inglourious Basterds was doing the build up/release thing then we saw many instances of that.
Committing wholesale to ripping off someone's creative analysis, even, or perhaps especially, if you try to dodge the simple word comparison service, and putting it out there is a cunt move on many levels ranging from depriving someone else (the one did the work even) of their audience to frustrating a meta analysis (if I am supposed to read the efforts of multiple reviewers to look for either interesting points they may have had or some kind of consensus opinion then that is harder). Should you get caught then expect the consequences to be incredibly serious, and you likely losing any kind of position as well as potential to hold a position.
Certain fields may well have some oddities and edge cases associated with them. Journalism, comedy, coding, patents, history, scientific research all having interesting things ranging from the humble meta analysis, coding is beset by problems detecting copying as there are limited ways to do things sensibly, general sourcing, for patents see the gillette defence or indeed almost any of the big defences and cases, and as sources is all important in history they have some things they do as well. For the subject of discussion here I fail to see any mitigating factor at play or defence that can be given.
I may well somewhere be guilty of the former thing, especially with the way my memory seems to work, but I can safely say I am not guilty anywhere of the latter, aspire never to be and can further say I have never even considered it. I did let someone copy my French homework once and help him understand what was being said and change the relevant words (he was blonde, I am not)... for which he got a better mark for despite no spelling or grammar mistakes on his or my part.