I'm a piano teacher. (A proper one I hope.)
You don't need a teacher for everything - you can learn a lot on your own, if you are determined to keep at it. If you give up easily, then trying to learn by yourself won't work very well.
The two best and most important things to learn by yourself are reading music and memorizing. These topics can be boring but are not very hard, you can learn them from books, and if you make mistakes in reading or memorizing you can just correct them tomorrow. And you don't even have to own a piano to do them! You can learn reading and memorizing while sitting in an easy chair.
How to work your hands and arms at the piano is the part where most people really need help from a teacher. Some people learn this by themselves too, but it's much harder than learning to read, it's hard to get it from a book because the books are hard to understand, and if you do it wrong you will waste a LOT of time, and could even injure yourself badly.
The people who get injured the most are the eager hard-working ones who think they are doing fine. They don't realize that they're pressing too hard, making their muscles too stiff, and so on. Lazy people don't get injured so often. (They might not learn much, but at least they don't get hurt.)
Please don't practice advanced-level music without help from a teacher. But if you show up to your first lesson with the new teacher and you already have a bunch of music memorized, you might turn out to be their new star student!