Until this morning, I didn't get much writing done this week. My usual goal is 750-1000 words per day. Other than a few quick sessions on my breaks at work, today was the first real writing I've done all week. Family comes first. There will be times you don't write for days at a time. Life intervenes.
One attempted writing session this week ended with me dozing in the chair, laptop open. I was just too exhausted. That happens. You can always come back to writing. It'll be there. That being said, if life isn't making you crazy, you should strive for a daily quota of words.
My wife also put things in perspective when I was whining about lack of commercial success. I'll paraphrase her:
"You're a writer. People like your books. Someone is interested in making a movie out of one. Keep writing. Who cares if you never get rich? Some rich people are assholes. Do you want to be an asshole?"