How can a supplication be sinful?

Muslim narrated from Abu Hurayrah that the Prophet, peace and blessings be upon him, said: "The supplication of any one of you will be answered as long as he does not supplicate for a sin or for the severance of ties of kinship, and as long as he does not become impatient." Supplicating for a sin means supplicating for something unlawful, such as supplicating for the killing of a Muslim, or asking for alcohol, or seeking forgiveness for a disbeliever who is known with certainty to have died as such, or for the eternal damnation of a believer in Hellfire, or supplicating with a foreign word whose meaning is unknown, or supplicating against someone who has not wronged him, or exceeding the bounds in supplicating against someone who has wronged him.