Think of it this way - any event, any happening you create for your story can be thought of as the smallest end of a cone - the rest of it, the ever broadening end of the cone extending out into the future. Sort of a writer's nirvana.
This allows for an infinite amount of events to be spawned or calved off from the original event - in fact, an ever-expanding array of possibilities. This is good for a writer.
BUT and it is a big BUT - while the possibilities are multitudinous the probabilities are more limited. That is, to remain a bit more within the area of reality. For example, characters you create for a romance novel could be kidnapped by aliens, whisked off in a spaceship and delivered to a new planet (yes, it's been done), but the greater probability is that those characters will be mistakenly arrested for shoplifting and delivered to the nearest police station.
So what's a writer to do? There are two routes to travel, either of which is fine as long as you keep your story on track. You can keep your characters and events more within the cone of probability, which will make your planning somewhat easier.
Or, you can step outside that cone and do something completely unexpected. The hitch with the second choice here is that if you do that every time you add a new element, a new cone of probability is created. Yes, that's true with the first route, writing more closely within the cone of probability, as well where you keep your characters and events more within that cone.
But, the more you stretch the parameters the more you, as the writer, have to be on your toes, to remain aware of the possibilities you are creating and where they may take your story. How your writing may have to be developed and altered.
No matter how you approach your story-telling you have to remember you must keep your world and your characters real to your reader. You must remain true to the world you create. I've said this before. If you have a knight riding to the rescue of a fair damsel and they're on the deck of a spaceship, you better have a mighty good reason that makes sense to your reader.
So, when you explore your cone of of probability, think about your possibilities, remember, as your starting out, what's more likely to happen to your character, then stretch out from there.
Some fantastic tales have been told from comfortably within the cone of probability - some equally great stories have been created by pushing the soft edges of that expanding cone to the max. You're the writer - the story you create is uniquely your own. Explore the probabilities and let your imagination take flight with the possibilities.