Why seven hundred and fifty words
Not a nice round number, and not an accident either. On the length that is long enough to get past yourself.
Seven hundred and fifty words is about three pages of longhand. That is the number, and the number matters less than what it is for.
The first hundred words are throat-clearing. You write about the weather, the to-do list, the thing you should have said yesterday. This is not the good part, but it is a necessary part — it is the sound of the pump priming.
Getting past the front of the mind
Somewhere in the second page, if you keep going, the writing stops being about things and starts being the thing itself. You lose track of the count. A sentence arrives that you did not plan, and it turns out to be truer than anything you set out to say.
That is why the goal is not fifty words, or a hundred. Those you can do while still performing for yourself. Three pages is long enough that the performance gets tired and wanders off, and what is left is closer to the truth.
The point isn't to write well. It's to write at all — and to find, page after page, that the writing has been quietly rearranging you.
And then you stop
The other half of the number is that it ends. Reach the goal and the day's writing is done; there is no bonus for more. A practice you can finish is a practice you will come back to tomorrow. That is the whole game: not one heroic session, but the next one, and the one after that.