It's "its," or is it?

It's said to be the most frequent error in language usage: its vs it's. And your spellcheck thingy won't catch it.

Neoneocon reflects:

The error almost always goes in one direction only: the use of the apostrophe, as in “it’s,” for the possessive form of the word, when it should only be used for the contraction “it is.”

In this, however, we’re following another rule (are you still with me? or have I already bored you to tears?), that of the possessive personal pronoun: hers, his, theirs, ours, yours, for example. All lack apostrophes. But they’re not confusing, somehow—perhaps because, unlike “its,” they clearly refer to people, and are never given an apostrophe because they never become contractions.Why do we do this?

Are we all just stupid! No, no, a thousand times no! We are actually very smart, because we are extrapolating a general rule to include this word, and that is the rule about forming possessives. Usually we do this by adding an apostrophe and an “s,” as you no doubt well know. But with the words “it’s” and “its,” we choose to reserve the apostrophe for the contraction, and that leaves the possessive hanging out there, alone and forlorn and apostropheless.

Oh man, hate it when that happens.

I make the mistake only by sloppy typing: the fingers are working but not the brain.