Worrying is a worry. Identifying a serious problem and taking rational action to analyze and mitigate it: excellent behavior. Identifying a serious problem, taking what steps you can to mitigate it, and recognizing that you can't do more: excellent behavior.
But worrying about things is a modern passion. To worry properly, you should worry in groups, large groups; you should identify something that could happen but doesn't have to; you should forget to read Kahneman's Thinking, Fast and Slow; and you should proceed to dwell on the topic, seeking to promote anxiety for yourself and especially for others; you should be very sure not to engage in rational (especially quantitative) analysis or heed the work of those who do; and you should abstain from all action that might make the problem go away.
Your anxiety will in the end go away, because the problem will most likely go away; or perhaps your fear will come true and you'll be in a different place; or else you'll be dead. You will have maximized your unhappiness and stress levels and, with luck, those of others, with nothing to show for it otherwise.
The ancients knew this behavior, of course, and the Greeks called it deisidaemonia and the Latins superstitio. They used those words to bracket behavior that led to no good. We've borrowed the latter word but applied it narrowly, to activities where anxiety cringes before the imagined divine. The ancients didn't need a broader category because the ubiquitous divine could be blamed for anything. We haven't got a better word yet to describe and deplore generalized cringing before what our own imaginations show us. We could use one. In the meantime, a broad awareness of the cultures and deeds of people and nations in our time and all the times before that we know of can be an excellent remedy for worry and an instigation to rational behavior.
There will be a lot of other essays on this typically intriguing Edge question that invoke worry and use the word easily—so should we be worried about that? Here's the test I would use to decide: If what my colleagues in these pages are talking about is evidence-based, especially quantitative, peer-reviewed or peer-reviewable, and has the effect of increasing our understanding and moving people towards appreciation of intelligent actions we can take as individuals or society, I'm not going to call that worry. And there will be a lot of it.
But if it's about the comet ISON veering off its path and plunging to Earth and there's nothing we can do about it—that's a worry we should worry about.