"I illuminate the moon with my heart, but the moon shines in the ditch" means that I treat you with good intentions, but you are indifferent and don't appreciate it. This means that his sincere efforts have not received the rewards and respect he deserves.
Source: Chapter 31 of Yuan Gaoming's "Pipa Ji", a few words of admonishment to the father - "No one asked under the window for ten years, and I became famous all over the world. I originally set my heart towards the bright moon, but what happened? The bright moon shines on the ditch."
Meaning: No one cared about me when I studied hard for ten years, but once I passed the imperial examination, I became famous all over the world. I originally entrusted my heart to the bright moon, but unexpectedly the bright moon only illuminated the ditch.
Extended information:
"The Story of Pipa" is a work of admonishing loyalty and filial piety. It is also a work with extremely rich ideological content and multiple themes. In ancient society for thousands of years, the Chinese nation has long formed and gradually developed social moral concepts such as loyalty, filial piety, justice, and justice, which contain both good and bad elements. The same goes for ancient filial piety.
In ancient filial piety, there is the absolute interest of safeguarding parents, requiring sons to make unnecessary sacrifices and obey slaves, such as "the father wants the son to die, and if the son does not die, it is unfilial." Or "cut off one's legs to save one's mother" and other foolish filial piety, which is bad.
It is virtuous and filial to love your parents, do good things to your parents, and dedicate yourself to repay your parents for their kindness in raising you, so that your parents can spend their old age peacefully. "Pipa Ji" is intended to promote virtuous and filial piety, the good side of filial piety, and the excellent morals of the Chinese nation. This has great practical significance for the construction of socialist spiritual civilization.
Baidu Encyclopedia-Pipa Ji