Are you talking about the acoustic piano or digital piano / keyboard? it is a fatal difference. On a digital piano, you can learn any C score and transpose the key with a click of your finger. Keys are abstract concepts (and quite recent in the history of western music). Learn to reason on the basis of the relationships between the notes. With an electronic keyboard you can also become a virtuoso by learning all the pieces in C and using the transpose button. Of course you need a rough idea of the other keys. However, you must resolve the question of modulation if a piece of music requires it.