Throughout the movie, it is clear that Daniel Plainview always does what is best for H.W. Be it giving him a respectable oilman name a la H.M.Tilford and J.J.Carter, be it pacifying him by putting whisky in his milk when H.W.'s father dies, be it bonding with H.W. over camping, hunting for quail, searching oil, be it keeping H.W. in the room when discussing serious business, teaching him about the business...Be it indirectly hooking him up with Mary Sunday, be it consoling him by singing to him when he first gets deaf, be it sending him to a school for the deaf in San Francisco, be it buying him a big, strong, expensive meal to put decent food inside of him -- Daniel Plainview is a model father to be emulated.
It is only natural that in the end he also, as a good father, needs to tell H.W. when he is wrong, a bastard from a basket in setting up competition against Plainview.
It is only natural that in the end he also, as a good father, needs to tell H.W. when he is wrong, a bastard from a basket in setting up competition against Plainview.