They're called typos. Everybody makes them — even professional writers. In writing that's intended to make money, they're usually caught in editing. If you yourself write without ever producing a typo, that's nice, but it's not really all that important to the craft of writing — much less to owning a business that employs writers.
At any rate, I don't see any reason to expect perfect prose in an informal context like a comment thread. As long as you're understandable, what do you gain from spending more time on nit-picky details?
At any rate, I don't see any reason to expect perfect prose in an informal context like a comment thread. As long as you're understandable, what do you gain from spending more time on nit-picky details?