In the first few years of piano lessons, many students develop a habit of learning their pieces hands alone before putting them together.
At first, it makes sense. Learn the right hand alone. Learn the left hand alone. That should make learning hands together easier, right?
No. It doesn't.
In fact, it ends up taking three times longer to learn the piece.
Think about it. Learning the entire right hand alone. Then the entire left hand alone. And then the entire piece two hands. It's like learning the piece three times.
Plus, learning hands alone does not make putting them together any easier.
Learning piano music hands alone is attractive because it appeals to our need for ease and comfort. And, it makes us feel like we're moving forward without challenging our patience too much.
But, it's also an example of how taking the easy way can end up making learning a whole lot harder.
The closest analogy would be trying to get in shape. Saying, "This week, I'll eat healthier. Then, next week, I'll work out every day. And then, the next after that, I'll put both together."
Wouldn't it be easier and more realistic to eat healthier and work out at the same time from the beginning? If you really wanted to get in shape, that is.
We need to break down challenges, no question. But, it's important not to get too far off the beaten path. If it's a two-handed instrument, use both hands. If it involves exercise and eating well, do both.
Anything further off, and you're not really practicing. You're stalling.