He was talking about Superman, and the quote comes from his comprehensive book - Superman: The Complete History. The quote reads: "It's a bizarre story, about a strange visitor from another world, but at its heart it's a very human story too, about the dream of having power, and the hope of knowing love."
Though Daniels was talking about Superman, I believe this quote can be applied to most superhero characters... Minus the "strange visitor" part.
The most important element is at the end: "The dream of having power, and the hope of knowing love." To me, that pretty much sums up what superheroes are all about.
I find it an optimistic quote because the most compelling part of the superhero story can be achieved in the real world. It's about finding impossible strength in whatever you decide to do in life, and finding that amazing person to share it with.
So, yes, it is possible to be a real-life superhero!