Michael, Ally, and True went to dinner. Michael ordered trout. Ally ordered steak. True ordered eggplant lasagna. Michael liked the trout, but he thought it was a little dry. Ally thought her steak was the best steak she had ever eaten. True thought their dinner was too salty.
Wait, what? Did True think that all of the three dinners were too salty? Did True sample a bite from Michael’s plate and Ally’s plate? That couldn’t be right, because True was talking about one dinner. No, in this case, True was a nonbinary person, i.e., a person who does not identify as a male or female. So, when True thought “their” dinner was over-salted, True was referring only to True’s dinner.
That True thought this about True’s dinner isn’t readily apparent, though, is it? That’s because of the ambiguity that is created when “they” and “their” are used to refer to a single person in the written language. “They” and “their” are commonly misused in verbal communication all the time, however. Almost all of us use those words incorrectly in casual speech. For instance, I’ve heard things like, “A patient has to take their medicine regularly,” or “That kayaker lost an oar in the water. Would you please reach over and get their oar since you’re closer than they are?”
That usage is incorrect, but, in everyday conversation, it’s the rare person who would correct it (I stopped doing this because I was told it was an annoying trait). However, as a copy editor, that is my job. I am paid to make sure that nouns and their pronouns/possessive adjectives agree. (I just learned about possessive adjectives about a minute ago. In the last example above, “their” oar is a possessive adjective. “Possessive adjective,” however, is a mouthful, so I am only going to use the word “pronoun” to refer to both pronouns and possessive adjectives from here on out. Please adjust.)
In my capacity as a copy editor, if someone wrote, “A patient has to take their medicine regularly,” I would be obligated to change it to either: “A patient has to take his (or her) medicine regularly,” or “Patients have to take their medicine regularly.” And I would be incompetent if I didn’t change “Would you please reach over and get their oar since you’re closer than they are?” to “Would you please reach over and get his (or her) oar since you’re closer than he (or she) is?”
How a person self-identifies is not my concern. However, I am very concerned with sentence structure. To be fair, alternative pronouns have been introduced, but they never took off, so “they” and “their” are being routinely bandied about to refer to one person, and I just cannot have it. It’s not grammatical.
Yes, language is a living thing and it evolves, and I’m all for that. My father refused to acknowledge that “ginormous” and “horrific” were legitimate words. Those words don’t bother me. I’m totally chill with them. And I’m very woke about gender expression. You can identify any way you want. But I will always believe that singular pronouns are for singular people.
There’s a solution out there. And when I’m crowned Pronoun Queen, I will find it.

I crown you Pronoun Queen!
If someone disagrees, it’s their problem! (just kidding, please don’t send the Pronoun Police).
Thanks, Boaz. I treaded a fine line on this one. I didn’t want to offend anyone, but I take pronouns very seriously and also deserve to be heard (in my opinion).