There is a specific moment, usually in the second or third month, when an adult beginner concludes that they are not musical.
It arrives like this. The right hand plays the melody. Fine. The left hand plays its part. Also fine. Then you put them together and something genuinely strange happens: the left hand starts copying the right, or it stops entirely, or both hands lock and you cannot make either of them move. You try again. The same thing. You try slower. The same thing.
Almost everybody decides, in that moment, that other people's brains do something theirs does not.
They do not. What you have just met is the most ordinary obstacle in learning the instrument, and it is a coordination problem, not a talent problem. It is worth understanding what is actually happening, because the understanding tells you the fix.
What is really going on
Your two hands are not two independent systems that happen to be attached to the same person. Early on, they are strongly coupled — which is why it is easy to clap, easy to carry a box, easy to do the same thing with both hands, and hard to do two different things. Every pianist starts coupled. What separates a player who can do it from one who cannot is not a property of the brain they were born with; it is hours.
So the question is not how do I make my brain do this, but what practice actually decouples two hands, and there is a real answer.
The thing that does not work
Playing the passage hands-together, at tempo, over and over, hoping it resolves.
It will not resolve, and the reason is worth knowing: at speed, your hands can only do what they already know how to do together. If the combination is not yet learned, every fast repetition rehearses the collapse. You are practicing falling apart, and you will get good at it.
What does work
Learn each hand until it is genuinely automatic, not merely possible. This is the step people skip. If the left hand still needs your attention to get through its part, there is no attention left for the right. Play the left hand alone while looking at the ceiling, or while saying the beat out loud, or while thinking about something else entirely. If it survives that, it is automatic. If it does not, it is not ready, and putting the hands together will fail for a reason that has nothing to do with independence.
Then go absurdly slowly, and make the joins conscious. Put the hands together at a speed where you have time to think about each moment where they coincide or diverge. You are not playing the piece; you are teaching your hands a map of who does what and when. This is why it must be slow enough to be boring.
Work on the seams, two beats at a time. Coordination does not fail across a whole line. It fails at specific junctions — the beat where the left hand moves and the right sustains, the bar where one hand has two notes against the other's three. Find that junction, isolate two beats, and repeat those two beats alone until they are dull. Then add one beat on either side.
Count out loud the whole time. Counting is what gives the two hands a shared reference. Without it, each hand is following the other, which is precisely the coupling you are trying to break; with it, both are following the count. This is the reason counting is not optional, and it is the most common missing ingredient when somebody tells me their hands will not cooperate.
Try one hand playing while the other only taps the rhythm on the lid. Strip one hand down to rhythm alone. It is far easier than full playing, it isolates the coordination from the notes, and it very often unlocks a passage in a few minutes.
Give it more days, not longer days
This is the skill where practicing often matters most and practicing long matters least. Coordination consolidates while you are away from the instrument — the passage you left in pieces last night is noticeably better tonight, without your having done anything. That effect needs the sessions close together. Fifteen minutes on six days will build independence that two hours on Saturday will not.
It also means that stopping while it is still not working is not failure. It is part of the method.
How long it takes
Longer than you would like, and less time than you fear. The first piece where the hands do two genuinely different things is slow and hard-won. The fifth is much easier. Somewhere in the first year most people stop noticing the difficulty at all for ordinary textures, and then meet it again the first time the hands have to do something genuinely independent — and that time they know what to do.
What almost never happens is that somebody who practiced this way for a few months found that they simply could not. If you are stuck, the probable cause is the step above that got skipped: one of the hands is not yet automatic on its own.
And if you cannot tell which hand is the problem
That is the genuinely difficult part of learning alone, and it is not a failure of effort. When both hands are busy, you cannot hear them separately — nearly every adult who records themselves discovers that the accompaniment is much louder than they believed and that one hand is quietly dragging.
So record it. Set your phone at the side of the keyboard so the camera sees both hands, play the passage that will not work, and send it. The written feedback is free, and it will tell you which hand is actually causing it — which is the one thing you cannot find out from inside your own playing.