Grammar Girl Quick and Dirty Tips for Better Writing
Well, although there's a difference not only in spelling, but also in meaning, the usage of those two words demonstrates it's not something to be dogmatic about.
Your correspondent recently talked about flicking the Vs at the retreating car of an opinionated parent, and she spoke of a freedom I could never have.
Just as the breezes of speech blow from the breast of the opinionated, so also the soul is tossed this way and that, driven forward and backward, and the light is obscured to it and the truth not seen.
But once she zoomed out and realized she was being a single-minded martyr, she could better fit her proposal in the context of what else was happening in the organization.