There are thoughts that take over.
You know the sort. You feel like you're dealing with things levelheadedly, and clearly, and rationally until The Thoughts come along and take up residence in your brain, front and center (or wherever the primary locus of concentration is), nearly obliterating all else. They don't let go until you manage, somehow, to purge them.
And sometimes that process takes the form of a message that you must sit down at your computer and write in a nonstop, keyboard-abusing blur, so impassioned are you with what you have to say. After you write such a message, you feel lighter, stronger, clearer, and you go about your day knowing you've won the battle against The Thoughts.
Unless you're me, that is, in which case you get only halfway through your day before the worries set in. You worry that what seemed like passion will come across as bluster. You worry that all of your attempts to set out rational arguments cushioned by honest caveats and admissions will seem just shrill and angry. And more than anything, you worry that the steps you'd seemed to be making in the right direction have now been completely undone by your clumsy backward stumbling.
But what's done is done, you remind yourself. You can't take back the message, even if the Recall feature in Outlook actually worked (which it doesn't). And although you think you may have botched the tone of your words or used 'fucking' one too many times, you're not entirely sure you'd completely want to take it back if you somehow could. You've said (however harshly) what something in you clearly needed to say, and you must find some comfort in that.
Besides, when you've already lost the war, what's the sense in trying not to lose more battles? You're done.