American novelist E.L. Doctorow said that writing is ..."like driving a car at night. You never see further than your headlights, but you can make the whole trip that way."
It’s OK to begin writing a story or novel and not know where it's going.
After reading a jolly good book, I'll often think to myself, "I bet they had a really strong idea of that story and where it would begin and end."
On second thought, a safer bet might be that the writer didn't have had a clue when they started the story that Mrs. Smith next door would end up dumping her house, car, cat and goldfish on her husband and taking off to the south of France with the pool guy.
Having said that, you may be writing a who-dunnit, or some other work that requires a carefully thought out plot, so that you know where you're going and can get from A to Z without losing your way.
I have a terrible time with plot, mainly because my characters never do what I want them to do. It's a dead certainty that they take on lives of their own and make decisions independent of their creator (i.e. me).
Many years ago I tried my hand at writing a thriller. I wasn't good at the genre. I gave it a go, clumsily plodding along, a bit like that game Cluedo where Colonel Mustard murdered Mrs. Peacock in the library with a candlestick. Eventually, my characters got so fed up with this bumbling and plodding that placed them in boring and stupid situations, that one of them walked out, slammed the door in disgust and went off to join the French Foreign Legion.
So how do I write? I have a terrible time with beginnings and endings, so I just start somewhere - maybe with a character, or a snippet I heard or have been thinking about that I like the sound of, something that will lead me into my story. It's a haphazard and risky way to start , certainly not with any structure in mind, but it is this not knowing, this sense of discovery, that gives the work momentum and pace, keeps me trucking along, because I want to know, 'what is going to happen next?'
Such a writing process requires faith, and that's grown within me over many years, faith I have now to 'wind her up and let her go ...'. Easier said than done sometimes because I get anxious, apprehensive, doubt my ability to put even one sentence together. But, as my Mom always used to say, 'The show must go on'.
Let your first draft go where it needs and wants to. There is ample time for the editing, shaping and plotting and structuring later on.
Let your imagination lead the way.