Over the course of writing a fair amount lo these many years, I've run into a lot of grammar issues.
My own, certainly. I'll be the first to admit that my public school education did not guide me well in the ways of grammar. Sure the basics, but once you get past the basics, there's a whole lot left.
I started really learning grammar when I started taking foreign languages. I write intuitively with English, mostly picking up tips and tricks from reading. But other languages? There's no intuition to be had (for me at least), so it becomes more of a scientific pursuit. Everything with a genus and species, connected with sure laws of that language, which once mastered can be flexibly ignored.
In my continuing quest to finally learn the English language, I've run into problems that aren't so nicely settled. They're not my problems. It's not me. It's English.
For instance, English lacks a generic singular. We have a neuter: it. But, when I'm trying to talk about a general person's ideas or behaviors, it's not nice to say, "It may think." We're not robots! "He may think," would suffice, but maybe I want to include the ladies. "She might think," maybe, but that might lead Instapundit to give it a #waronmen tag.
The old standby was to assume the masculine. Everyone is a he unless otherwise noted, and, like with the Greek, a group of guys could mean all guys or a mix of guys and gals. Mankind, for instance, isn't just for men, but everyone "man-like" in a genetic/clinical sort of way.
You don't even need a kind, just Man suffices. "How to serve Man" was a cookbook for how to eat people, not just humans with penises.
That's not acceptable anymore. We say humanity now, or the tortured 'humankind', instead of mankind.

"All men are created equal" isn't allowed, as we want to say everyone has equal rights no matter what parts they have below.
Did you notice what I did in that last sentence? Each person (a generic singular) has rights, no matter what... what....
What pronoun is appropriate to press on in that sentence?
If you're old-fashioned you use just the "he" or if you're enlightened just the "she." Some use "he or she," but that's a sign of indecisiveness, and that's something I will not abide. Which is it?!
Admittedly, in our contemporary world "he or she" might even be an appropriate label for a specific subset of people. We're not talking about hermaphrodites, however, in our generic sentences, we're trying to talk about a specific, yet not specifically gendered, person.
Picking one or the other satisfies the need for a singular pronoun, and we all know a person isn't limiting the discussion to one gender. But this brings its own problems.
So, I've gotten into the habit, along with many others, of using the plural "they" as a singular. Which doesn't fit any rule but does fit how language has adapted itself to fill in missing gaps. Like with memory, it may not be correct but it does allow us to function.
A number of people
disagree. But
they're wrong.