And a more proper explanation of the title would be:
Do you often press “reply” or “quote”, type something and then realise that “nah, that wouldn’t make sense/be proper/isn’t as fantastic as it sounded in my head” and then just press “back” or whatever instead of posting?
I do. Quite a lot actually. I get these impulse urges to make a snark or comeback, which then don’t make that much sense at all when I see them in writing.
Yeah, nine times out of ten.
I do a lot, too. For every one post I make there’s around three where I get 3/4 done with typing only to say “Eh, what’s the point?” and delete it.
Sometimes, especially in GD and GQ, I type something out, then say “Eh, it’s not worth the argument…”
I predict this thread will have very few responses. 
And yes, I did have to struggle not to just hit the Back button on my browser.
Maybe one out of every three or four posts. I get to rambling, and then just like the OP writes, it “isn’t as fantastic as it sounded in my head.”
Of the posts I do end up making, a strong majority are recast after originally being ridiculously wordy.
Given some of my posts you’d think I don’t, but I actually delete about 9 out of 10 before posting.
I did it in this thread.
Yup. My cost count and year of joining make this pretty clear. I don’t post quite often.
Most times it’s just, “nah, not worth it,” or else it’s “meh, someone else just said what I was gong to say.”
Yes, I do that at times.
But, apparently not that time.
If I start typing, generally I’m going to hit “Post” (see). However, I often compose brilliant responses in my head, but are too lazy to type them out. Or someone will post a similar, but more eloquent response before I get to the end of the thread.
This may be one of my longest posts
Great, you used up your one in ten on this thread. Now you have to go agonize nine more times before you can do a real post. 
And yeah, I do that a lot, too.
Quite often. Especially if it’s some TMI thing since my mom posts here too.
Yes, happens a lot.
Yes. I should resist more often.
I’m glad I’m not alone in this then
…
All the time. Usually it’s a conscious decision to battle back my bad habit of questioning somebody’s belief merely to see how they respond. Part curiosity, part snark, part devil’s advocate.
Frequently, as well, I find that the reply I’ve typed up doesn’t pass my internal SDMB filter. Sometimes it can be fairly intimidating to post in threads, particularly debates in which conversations often devolve into a page-long point by point refutation.
That being said, there seems to be a divide in posters between a formal style of writing and a more conversational style.
Probably not nearly often enough, I’m sure.
Joining the chorus of “I do this all the time”. I have a Repository of Lost OPs on my hard drive, just waiting for the day that I feel strongly enough about one of them again to reword and post it.