铅笔写不出的未来橡皮擦不掉的过去
[qiān bĭ xiĕ bù chū de wèi lái xiàng pí cā bù diào de guò qù]
A pencil can be erased easily which is used here metaphorically. The future cannot be planned with certainty; no matter what was sketched using a pencil in the present, it may all end up uncertain in the future ('can't write'). And even if one tries to erase or ignore the past like how we might erase pencil writings with an eraser ('rubber'), the essence will linger and impact the user forever ('the past can't be erased').