It would take me literally 10 hours to write 10K a day, and that would also mean consistent concentration during those ten hours. Honestly? I've done more than that in one day, but my brain was mush and I could not sustain it day after day without hating the work for it. For me, 10K is too much in one day unless it's a one-time thing and I'm up against a deadline.
Everyone is different. I know authors who don't also work another full time job like I do and they write 10K a day. I also know authors who do nothing but write, and yet they are thrilled if they write 500 words a day. I think the key to having a word count goal is the same as any other goal. First of all, it has to be realistic And when you're talking word counts, you
are the only judge of what is realistic for you and your unique circumstances.
I'm familiar with Rachel Aaron's article. Her reasons for wanting to increase her daily word count might not apply to everyone. The worst trap you can fall into is thinking you have to keep up with someone else, or strive to write as much as they do, in order to be successful. Not true.
Be happy in your own skin first, and then figure out what is a realistic, sustainable word count goal for you. If you try to mimic someone else simply for the sake of doing so, you've already set yourself up to fail because that's not a healthy reason for motivation.
My daily goal is between 4 and 5K, but it took me over two years to find that "magic" number for me. Most of the time, I'm lucky if I reach 4K a day, but if it's clean work and I'm happy with where the story is going, then I've done a good job with those 4,000 words. I'm constantly readjusting my writing schedule to allow for things that happen to keep me from achieving my word count goal that day. It's called life.
Some things I can control, others I cannot. And there are days when I simply cannot get into the right frame of mind so I take a break from it. That's necessary, too, or you'll burn out quickly.
Hope this helps.