Metallica guitarist Kirk Hammett credits the band's personal growth for his debut solo release of Portals. While chatting with Kerrang, Hammett explained how the new EP came to be through his own sobriety and the band's maturity. He touched upon how former-bassist Jason Newsted's 2001 exit came about, in part, to his wanting to pursue a solo project away from the band.
Hammett compared the difference between Newsted wanting to stretch his wings and him doing so today: “It is 20 years later and Metallica have gotten even bigger since then. So trying to divert any kind of focus at this point, it would take an army to do that. And it's just good ol' me. And also we've all grown. We've all grown from our experiences and we've certainly grown from (Jason Newsted’s departure). It's a recognition that we're all musicians, we're all artists. Who's to say to someone else, 'Don't put your art out there, I don't want you to'? We've all grown up, basically.”
He went on to say, “So the question is, were we not grown up back then? Of course not. We'll be the first ones — or at least I will — to put my hands up and say I only feel like I've reached maturity in the last 10 f***ing years. Also I have to say I've been sober for seven-and-a-half years now and my mind is in a different place, I'm better focused. I got my brain back, I've gotten my memory back so nowadays I'm in a better place. I record music and my focus is that much better.”