I suppose the first question is, is it really necessary?
It’s a actually a tough question to answer and one that’s highly debated amongst writers but I’ll give it my best shot.
The way I see it, an outline of a novel or a short story isn’t a ‘written in stone’ requirement. It’s definitely a handy thing to do, but whether you choose to or not depends on how your brain handles creativity and what kind of writer you are. After all, we’re all different so what works for some won’t necessarily work for others.