It drives me crazy when people use it's to mean its, and I do not understand why they do it.
Because it is one of the most grating flaws in the language. Whether I say its or Clippy's when trying to indicate ownership depends on whether I wish to use its name or be generic. The ad hoc rules of grammar that we use are a kludgy hack and this is the most annoying kludge.
I personally choose to use the prescribed grammar. Defection would be pointless. Yet while I am usually rather particular when it comes to spelling and grammar this is one instance in which I have more respect for those who use "it's" in error than those who indicate contempt for and incomprehension of those who do not understand the mistake.
Apostrophe rules are scatterbrained, but I'm not sure how high they be on a list of grating flaws or kludges in English. I might not even have made them a separate list entry; they're a subset of homophones, and many other homophones are more detrimental to clear communication. Non-phonetic spelling rules make it harder for everyone to learn to read. Irregular conjugations add unnecessary and illogical hoops to jump through before anyone can even speak without unintentionally signaling low intelligence. Hell, I used to think of I/l/1 as a programmer's problem until I discovered that toddlers stumble on the same unnecessary ambiguity; at least programmers get to choose their own fonts.
There's been a recent heavily upvoted and profusely commented post about things people want to learn. It's close to having so many comments in a single day that it should probably have a part 2.
However, the subject seems to inspire thoughts about what *other* people ought to know, and while that's got a good bit of overlap, it's emotionally rather different.
So, what do you think other people ought to know? Any theories about why they haven't learned it already? Any experience with getting someone else to learn something when it started out as your project rather than theirs, especially if the other person was an adult?