A wise quote that I like very much.
There will always be problems... not matter how hard I try or how well I do. There are too many things in the world that is beyond my control - at least, I can control my reaction, if I am wise enough. And what is life without problems and challenges? It is an opportunity to grow and to be wiser. If you do not learn from the problem/challenge, it will always be back until you learn how to handle it.
And if you are mentally prepared to handle the worst case scenario, you can handle almost anything fearlessly.
Today, a colleague asked me "Why are you still able to smile?"
My reply was "That's the best thing to do now."
It is free!