A good reader interested in the premise of your story will beat himself up trying to figure out every character, every motivation, and each mystery in every plot you present.
Don't make his pain worse by having no idea what you're doing either.
Outlining where your story is going will not only help your reader, but help you. You will be able to chart the direction of your characters, and you will get a lot less frustrated.
That is, if you have an idea what happens next, then you won't get writer's block, pull out your hair, and destroy your computer.
Which you definitely don't want. Don't write yourself into a corner!
So, what do you do? What is outlining?
1. Estimate how long your book will be. Give yourself a target. 50-75K words is good for most novels.
2. Consider your main character, and decide where you want them to end up. How do they start, and how do they end? Emotionally as well as in the plot.
3. Consider any major villains, love interests, or major secondary characters and do the same thing. How shall you weave them all together?
4. List out some set pieces you want to use. A trip to the mountains, a fight at the docks, a strange dream sequence...? Try to figure out some big arenas for the turning points of your drama, then try to put them in rough order.
5. Map a few chapters ahead. Know where you're about to go. You don't have to know every chapter at the start, but outline a few chapters at a time. Be sure you're heading in a good direction. This also allows you to foreshadow, because you know where to drop your hints.
And with that, you should be just fine! Remember, err on the side of planning, not on the side whimsy. Of course as you write, new and great ideas will take shape that overrule your plans. It happens to me all the time. But be REALLY SURE they are great ideas before you roll with them. Just think to yourself: What am I doing, and is this a good idea?
Which is a good life lesson in general!
No really, it is!
*Yes I like Star Trek. Spock is my waifu.