Is he doing it himself, or is he working with a partner? If he is struggling to feed one person, keep in mind that as an author/artist combo you'll be struggling twice as hard to feed two.
If you're determined to take the chance, at least be very smart about it. Figure out how much money you spent in the last year (rent, food, clothes, car, internet, spending cash, ALL of it). Keep your day job until you have that much in your savings. THEN quit the day job and go forward.
"Starving artists produce the best art" is a myth. You'll do your best work with a net underneath you. If you don't have a decent savings already, make that your goal to be your motivation.
And in the meantime, you can always "practice" at the life you want. Take a day or two off from work, give yourself a 3 or 4 day weekend, and spend 8-10 hours a day for all 4 consecutive days just writing/networking. People think it's gonna be great to work all day from home until they do it. I worked freelance for about 5 years and it is much more emotionally taxing than a lot of people think (as I'm sure your friend can vouch for). If you already feel that you need an outside "push" to get you there, you're going to need that push again and again and again.
It's not unattainable and we want you to succeed, just in a smart way.