There are a few phrases that I find helpful to repeat to myself during difficult times. All of them are things my sisters have said to me at one time or another. I found myself sharing them with a friend recently and subsequently decided to share them here.
1) This isn't your new life. This is for when your problem or situation is so hard or overwhelming or lingering or agonizing that you can't imagine that you'll ever not feel this bad. Well, that's just not true. Overwhelming and agonizing is not your new life; it's just right now and it inevitably won't be like this forever. There exists a place where you're not struggling and it's called the future.
2) You're just a person in the world trying to work something out. This is for when you're beating yourself up over your situation or thinking that your problem or struggle means that you're bad or wrong or dumb. It's to remind you that you're just a person, doing what people do--that is, make tough decisions, react to tough luck, manage stress. It's life and you're living it and you're probably doing the best that you can.
3) Look out the window. This is for when what's going on is so all-consuming that you're living 100% in your head, going around and around with your thoughts, and can't stop. Looking out the window--literally--allows you to remember that there's a world out there beyond your problem. Look! That woman walking by doesn't seem too concerned about your situation; in fact, she seems to be enjoying the sunny day. This isn't a suggestion to just forget your worries and enjoy spring, but when your mind is simultaneously stuck on overload and repeat, looking out the window and noticing that the world is still turning can break the cycle.
4) No one decision can ruin your life. This is for when you have to make an impossible decision and are worried that the wrong choice will ruin everything. Yes, of course, decisions about whether or not to move, whether or not to get married, whether to take one career path or another, and other big choices are important. And yes, they will impact the direction your life takes. But no one decision can make or break your life. That's just not how it works.
These might not all work for everyone in every situation, but they're worth a try.