Bob Marley countered: "Don't worry / 'bout a thing / 'cause every little thing / gonna be alright."
As prognostication, it's hard to say who's correct. As a guideline or mental outlook, pessimism and optimism both have their merits. Psychologists have shown that if you imagine a particular worst-case scenario but then envision yourself surviving or transcending it, that can have a salutary effect. I guess this would be called a modified pessimism. It's a technique best invoked in the particular, though. As a general mindset, I think optimism is better. Norman Cousins wrote that:
the main characteristic of pessimism, like cynicism, is that it sets the stage for its own omens. It shuns hope for the future in the act of denying it. It narrows the field of vision, obscuring the relationship between the necessary and the possible.