What you did comes back to you, and no one else did this to you; 得 is to receive, so the fruit is received, not gained. The words are a sutra's, translated into Chinese in 539, where a hell-warden speaks them to a sinner wailing in the fire, and asks him why he wails; a Japanese monk wrote them of himself about 1213, and Hakuin sang them to mill-girls in 1760 with the seed and the field, which is where the English harvest meets the Japanese.
The sutra says it of good deeds too; Japanese usage says it of bad ones, so the words are a warning in Japanese and can be a promise in English.
We want you to be as happy with the meaning as you are with Master Takase's art. To learn more, visit Philology of 自業自得.