You can strip away many unnecessary troubles which lie wholly in your own judgement. And you will immediately make large and wide room for yourself by grasping the whole universe in your thought, contemplating the eternity of time, and reflecting on the rapid change of each thing in every part - how brief the gap from birth to dissolution, how vast the gulf of time before your birth, and an equal infinity after your dissolution.
All that you see will soon perish; those who witness this perishing will soon perish themselves. Die in extreme old age or die before your time - it will all be the same.
Getting the right perspective on things is, in my opinion, vital to living a life of contentment. I've not read the book, but from what I can tell of the title, it deals with having the right perspective. The book is called, Don't Sweat the Small Stuff ... and It's All Small Stuff: Simple Ways to Keep the Little Things from Taking Over Your Life. A phrase I've often heard, that is also appropriate about learning perspective, is, "don't make a mountain out of a mole hill." If you find yourself constantly wringing your hands over big events, small events, unexpected events, life changes (big and small), people, money worries, health worries, etc., etc., then you need to get some perspective. Hence the Stoics would often practice contemplating the vastness of time and space and view their lot in all of it. Once we see how small we are in time and space, those worries get really small, really fast.
For me, one of the best ways I've learned to help myself keep that proper perspective is to be a student of history. I bounce around quite a bit on the historical timeline. But I've read books about ancient Greece, to books about World War Two, to books that talk about the Golden Age of Piracy. And each of those books are filled with stories of people who've lived a lifetime full of wild, fascinating, arduous, beautiful and harrowing experiences. And then to think about all the complex and extremely deep history this world has and contrast that to the countless planets and solar systems and galaxies and possibly what history they may have ... it's mind-boggling to say the least. How tiny and small I am and how insignificant my worries are.
And still after you realize how tiny and small you and your worries are, the constant reminder of: after all is said and done, we all die anyway.
Lastly, some advice about how morbid and depressing these thoughts may be. To the contrary! You are alive now! You can choose what you will do and how you will live. The exercises above are merely to help you get over it and start living! As Marcus says, it "make[s] large and wide room for yourself" or it gives you some space to focus on things in your control. Don't live your life all wrapped up in worry and anxiety - look beyond that and do your part to add to the complex and enduring story of human history! Indeed, carpe diem!
(see also Citadel p. 172, 254)