When we're kids, we want to know about everything. A pile of books checkout of the library run the gamut from the Narnia series to a book on lighthouses, to one on cats, to another that explains how to do magic tricks. We're sponges when we're kids. It's all new.
And then, we get sort of full up. We get busy, school gets harder, we have to learn all sorts of stupid little rules about how to get by in life, from how to keep our boss on our side but not kiss her ass, to how to keep our loved ones happy without losing our minds. And then there's retirement planning. We get jobs, and we have to do stuff that's boring or repetitive. And the world just seems so damn sad and tragic and overwhelming. Turn on the tv, you get caught up in the most recent war and disappeared kid and abuse and inequality. You lose the urge to find cool stuff out because, somehow, all of the cool stuff is buried under shit, and you have enough shit in your life to deal with. You can't bear the thought of adding any more to it.
You can't be a writer if you're not curious. Otherwise, you'll end up writing about your own life, and what's the fun in that? We already live our lives, and everyone else lives theirs. Navel gazing is for amateurs.
(This isn't to say that using stuff from your life isn't good when writing. 'Stuff' as in the feelings of panic and heartbreak and frustration and joy and wonder, the themes of relationships and family and work...just not, you know, autobiographically. No one, really, wants to hear me go on about my lousy little life. If something amazeballs has happened to you, write notes on it, keep it in a notebook, and write a memoir one day. Otherwise, just keep the rest of your stuff in the vault. You'll grow as a writer with practice and one day learn how to use this stuff without it being all David Copperfield/Holden Caulfield-ish.)
Anyway, back to curiosity:
Little kids have the right idea. Learn how to be a sponge again. Ask WHY. Ask HOW. Ask WHERE. Turn off your phone, put it back in your pocket, and come up with an explanation for WHY that lady on the train is putting on her make-up now, for WHY the old dude sitting near the window has a skateboard in his bag. Ask HOW people first figured out how to bake bread, or HOW to make plastic, or HOW to rig a 17th century galleon. Ask WHERE that family of four--all dressed in winter coats & hauling luggage--is going on a warm September day. If you're not curious about the world around you, you're going to end up on the carousel that's inside your own head, going round and round and looking at the very same scenery.