Try to resist the urge to plan out your idea extensively by working out every eventuality before you start to draft the narrative.
When you begin the writing of a novel, you may have a notion of certain plot events, maybe even a potential ending, but it is likely that there will be large gaps in the narrative that you do not yet know.
Trust your idea enough to leave them there.
Write towards them, and when you get to these spaces, listen to what your interest and your instinct is telling you at that moment. The plot should always have the capacity to surprise you, the writer, just as you hope that it will your reader.
Trust in the fact that if you understand your characters intimately enough – their relationships, their history, their motivations – then most of the work of ‘plot’ will be done through characterisation. Because what is interesting is not so much how events lead characters, but how characters lead events.
And if, on reading back the narrative you developed using your instinct, the plot doesn’t yet feel quite right, that is what redrafting and editing is for.
The plot should always have the capacity to surprise you, the writer, just as you hope that it will your reader.