I can understand where the question comes from, though. During my past writing hiatuses I haven't been inundated with story ideas and just thought "Nah, I'm not going to do anything with that." During those times, I'm not consciously aware of many, if any, story ideas. So for those who don't write, I would expect that the same would apply. They never have that "Oh!" moment where a writer starts thinking "Hey, I could do something with this idea." And it's not because they aren't creative or aren't smart or anything like that. It's because they aren't thinking in the mindset of a writer.
A lot of my ideas for stories come from a passing comment someone makes, or a small bit of information I read or hear somewhere. Sometimes the ideas come from thinking about something that's actually happened to me and having that "Hmm, what if...?" moment. Very, very few of my ideas come from consciously sitting down and saying "I'm going to think up some story ideas." What's happening here is that the initial stimulus -- whatever it was -- acts like the grain of sand at the center of the pearl. It's that mindset of a writer that then builds the pearl around the grain of sand, adding details to the original concept and fleshing it out.
So we've hit on some important points here.
- Ideas are all around us, but they usually don't present themselves as stories, only the stimulus.
- Having the mindset of a writer to latch onto those stimuli and build the pearl around them is absolutely critical.
- The initial idea is (usually) only a small part of the final story. There's lots of work still to be done, even for a short story, let alone a novel.
If you're working at being a writer and find yourself struggling to come up with ideas, I'd suggest several things:
- Try not to "stress" about it. I realize that sounds hard -- like not thinking about the elephant -- but for mental work like writing stress is frequently unproductive.
- At the same time, do try to keep your brain open to the seeds of ideas which are around you. If something interesting catches your eye or ear, give it an extra few minutes to roll around in your mind and see if anything develops. If nothing does, that time, that's OK! Give it a try another time with a different stimulus.
- If you're prone to forget an idea you had, make sure you have some way of making yourself a note about any ideas you develop or that you want to mull on at a later time. A physical notepad is one option, sending yourself a quick email from your phone is another option.
- Finally, if you're feeling completely stuck and none of these ideas have worked for you, here are two more ideas: 1) There are blogs and websites with specific writing prompts. A Google search should help you find these. 2) Alternatively, you could try just starting typing. Type anything. See where it leads you. Maybe the first couple hundred words will be junk, but if it gets you pointed in a new direction, that's a small price to pay.