HAPPY ENDING?

Its actually been a month of Sundays since I was working upon to finding out the real meaning provided by the combination of these two words.
Is it necessary that endings should always provision happiness?

To me,this thought is something really very confusing...How can endings be happy?
Although,its the end..The last moment of something and you're not going to experience it or have it anymore in the journey forward.
You may have a happy start or a middle.But a happy ending?

I've gone through articles or quotes of many upon this and they state that end can be happy or sad,it actually depends upon where you stop.
How can I stop my story according to my wish?

Then,
WHO/WHAT is destiny?