Some people have a problem with starting a story. I don't. I have a problem with finishing them. I know where I want to go, but getting there can be a problem. One technique that I've learned to use is called bringing it to a point. If you have closure issues, it might work for you as well.
I write like I paint. There is stuff everywhere. Okay, and maybe badly. Regardless, the storyline that starts out in detail quickly ranges to and fro like a ship on a storm filled sea form some great Viking yarn. I used to fight it, but now I just go along for the ride and hope I'll find myself with some great story of value. Sometimes the boat finds the promised land. Sometimes it sinks! Regardless, it is an opened ended form of writing that can go as long as you can write. What if, however, you know the destination, but can't see how to get there. You need a technique to develop this process in your mind.
The technique of writing to a point is admittedly a simple one. Perhaps it is even infantile. All I know is it has helped me with this issue. So, how does it work? The answer is in structure. Pick a predetermined length of text you are going to write. I usually go with five or 10 pages. Now nail down your ending in a short paragraph. Write it on the bottom of the last page. You know have your point.
The rest of the exercise is pretty simple. Start writing on the first page and practice bringing your story to the final paragraph. Will you will rarely, if ever, pull this off. You also do not need to worry excessively about grammar, punctuation or any such thing. None of these things is the point, pun intended, of the exercise.
To me, a story is an arc. It starts here and ends up there. The point of this exercise is to train yourself to deal with the last part of the arc. You've written to the highest part of the arc. Now, how do you bring it back to a defined finish...a point if you will? Frodo Baggins went underground, over water, through marshes and so on. From the word go of the story, however, he always had to complete an arc that found him in Mount Doom.
Many stories succeed or fail in how they close the arc of the story line. Getting from here to there is obviously important, but it is often the last 100 steps that make the journey a success or failure for the reader. Using the bring it to a point technique is one way to practice making those steps worthwhile in your story.