Final answer:
The irony in the lines adds humor to the text by portraying the character's failed attempts at committing murder and blaming destiny for the failure.
Step-by-step explanation:
The irony in the given lines is that the character has tried to commit a murder, but has failed on both occasions. However, the character believes that it is not his own fault, but rather the fault of Destiny.
This creates a humorous effect because the character is blaming Fate for his own inability to carry out his plan successfully.