Not only the notes and rhythms might be incorrect but the articulation, fingering, pedaling, and the general feeling is not there.
The piece might be quite easy and you can be a very good sight-reader but the music isn't yours yet. It's the composer's. It hasn't sunk into your being.
Yes, the audience might never notice this but it's you who can't be easily deceived. Deep down you know how far it is yet to go.
It's frustrating at times to know the music from videos and recordings and to have heard the masters play them so well and not to be able to play it at that level yet.
What some people do at this stage is quit and go watch more TV or surf social media. It's because of this fear of failure we all face: "If I can't play it right away correctly it must be something wrong with me or my practice method".
It might also be out of fear of success: "If I succeed one day at learning this piece like masters do, I will have to act like a master." It's terrifying.
But what other people do is they understand that they are going to suck for 10000 hours anyway. They're in this game for the long haul. They know what it feels to be miserable at something and they love it.
They love each moment of this experience because it shows them the truth. The truth about music, the truth about the composer, the truth about the instrument, and the truth about themselves.
The truth can be painful but it liberates.
The only things worth doing are the ones you are not good initially.