Relationships. Real life situations. Whatever it may be, accepting it is the key to moving forward.
It is what it is.
This is the way things are.
You may have tried your hardest to make the outcome different. You may have tried your hardest to fix it. You may have done nothing and let things roll into place. Perhaps it is something that came out of nowhere. Something unexpected.
No matter, you must take it and accept it.
Accept it with your full being. Even if you do not understand, accept.
"Buddhist teachings on happiness have long held that accepting that which cannot be changed or controlled is key to reducing suffering."
So, let go of what you can not control, accept what it is, and decide how to move forward.
Move forward knowing that you can make it work. Move forward knowing that you have accepted what is and now that you can make it work, you got this! You got it, Happiness!
HERE is a great article for more inspiration.