I just love this one.
Sometimes we forget that there is a reason for everything that happens. We may not know what that reason is, or understand why something has happened or is happening, but having faith in the future is just what we have to do.
We just have to believe that someone has it all under control. In my case, it is God. Perhaps in your case it is God too. But whoever it is that you believe it, we just have to remember that He has it all under control.
And YES it is one of the HARDEST things you have to do - have faith and believe.