There's a saying in German that goes, "It's all in the how."
What I take this to mean is that we often do not have any control of the "what" of our lives. We don't have any say about the weather, or the economy, or how other people behave. What we do have dominion over is how we choose greet these experiences.
As Deepak Chopra wrote, "you and I are essentially infinite choice-makers" (The Seven Spiritual Laws of Success, p. 40), and while we may not be aware of it, we are making choices in every moment of our lives. The choices we make in each moment affect our quality of life as we move forward from one moment to the next. Greeting an apparently negative or unpleasant event with sturm und drang will only create more stress and turbulence. However, making the choice to greet that same experience with conscious awareness can lead to much happier outcomes. This practice is especially useful when dealing with those things that repeatedly upset us.
If you can factor into your daily life that eventually (and probably very soon) some event will take place that will fall into the "habitually upsetting" category, you can consciously plan ahead as to how you greet that eventual experience.
For example, if you know that being late to appointments causes you a lot of anxiety, you can factor in the possibility of heavy traffic preventing you from getting to where you want to go smoothly. In anticipating this triggering experience that will probably activate stress and anxiety, you are preparing yourself to respond consciously, instead of reacting automatically. You can even discuss this with yourself beforehand like this:
"Okay, so I'm getting a bit of a late start to work this morning. I hope the freeway is clear, but it might not be. I don't have any control over that. But if there's bad traffic, I'll just remember to breathe and enjoy my drive. I'll try to live in the present moment, rather than predicting a doom-and-gloom outcome. Besides, I haven't been late, yet!"
If it turns out that there has been an accident, and traffic is really slow, then you have the opportunity to be consciously aware of any automatic thoughts that might be triggered, such as, "This always happens to me! I'm gonna be fired! What a loser!" When these thoughts become known, we can see them for what they are: thoughts and not facts. They are just another event that we can become aware of, but we don't have to give into them or even believe them. (And besides, they're not true most of the time, anyway.)
And of course, if traffic does go smoothly and you get there easily and in plenty of time, all the better because you haven't stressed yourself needlessly.
By practicing this kind of preparation, you can be ready for the emotionally activating triggers that will inevitably come your way. With diligent practice, new habit patterns are formed, and we move through life less re-actively, and more gracefully, with much more happiness and ease.
So while we can't change or fix the "what" of things, we can certainly have some say in the "how" of our response to it.