铅笔画不出的界限橡皮擦不掉的回忆
[qiān bĭ huà bù chū de jiè xiàn xiàng pí cā bù diào de huí yì]
This implies there are boundaries or limitations that cannot be drawn (or defined) by mere effort like writing with a pencil, and memories (like pencil marks) remain indelible no matter how much we may wish to erase them. It's about unerasable memories or feelings.