Where was the relationship between lord and warrior heredity?

The relationship between lord and warrior was hereditary in feudalism. A lord would grant a fief (land) to a warrior in exchange for military service and loyalty. The warrior would then become a vassal of the lord, and his heirs would inherit the fief and the obligations that came with it. This system of inheritance ensured that the lord would always have a reliable force of warriors to protect his lands, while the warrior would have a secure source of income and a place in society.