>It's extremely vague. It's like saying, "I wish to turn a screwdriver five hundred times today." It's reasonable to ask, "For what purpose are you turning the screwdriver?" ... what terminal goal are you trying to achieve with this journal? And why is necessary for you to write > 500 per day to achieve that goal?

On the chance that you are asking these questions in good faith, I can point you to a very deep and well written counter argument to your stance. Among his 20 or so other books, The prolific Japanese Author Haruki Murakami has written a book: Novelist as a Vocation. I encourage you to read it in whole, as my attempts to summarize will only take it out of context and butcher it. However, I will say that Haruki lays out the personal opinion that for him consistency is the bedrock of his writing practice. That above all, he sees writing as a daily commitment. He strives for 2,000 words a day. He typically takes on one wholly creative work at a time, such as the next novel. On days he just doesn't feel passionate about that project, he will translate works from English to Japanese until the passion for the project naturally returns. He makes the argument that the days he spends translating give him time to think and digest the next steps in his novel while also allowing him to keep a whole collection of "writer's habits".

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You can argue that his methods don't seem right for you... but you can hardly argue that his methods aren't right for him (and perhaps others).

It's in the article. Literally under the "Why" paragraph.