Why does the astrologer think that he has committed a murder?

The astrologer carries a great burden of guilt for many years. He thinks that he committed a murder long ago, because he stabbed his acquaintance and then took steps to ensure that the latter would not rise again.
After stabbing the man, the astrologer pushed his unfortunate victim into a well. He imagined that his actions rendered the wounded man powerless to escape from the well.
The text tells us that the astrologer was drunk on that day. This could have played a part in his perception of the unfortunate incident. In the story, the astrologer learns a stunning truth: his victim did escape, after all. It was only the coincidental appearance of a stranger that saved his victim's life.
Of course, the astrologer had no knowledge of this. It is the main reason he believes that he committed a murder long ago. Because he feared being discovered, the astrologer ran away from his village. If he had stayed, he would have tilled the land, like his forefathers before him, and grown old in his ancestral home. The story ends with a stunning resolution: not only does the astrologer discover his innocence, he also manages to evade the clutches of his vengeful former acquaintance.

Years before, the astrologer had brutally stabbed a stranger and thrown him down a well, leaving him for dead. It's not really surprising under the circumstances that he felt he'd murdered the man. Ever since that day, the astrologer has had to live with a crushing burden of guilt, believing himself to be a murderer. It's only when he finally comes face to face with the man he thought he'd killed that he realizes that his would-be victim survived, saved by a passerby.
Ironically, the man seeks the astrologer's assistance in finding the man who attacked him; he doesn't recognize the astrologer as his assailant, but the astrologer certainly recognizes him. Despite the tension of the situation, the astrologer is able to do the job for which he's being paid without revealing his identity to the man he attacked all those years ago. But he reveals his true identity to himself: a man who really isn't a murderer after all.