The father and son, in Cormac McCarthy's novel The Road, travel together in a post-nuclear holocaust world. While time after time they find nothing but death, isolation, and struggles, the father wants his son to continue on. At one point in the text the son states that he wishes he was with his mother (who committed suicide based upon her hatred of the world as it was). The father tells his son to never say anything like that again.
That said, the father, most likely, desires that his son experience life based for a couple reasons. First, the father repeatedly flashes back to his own childhood, a time filled with good and positive memories. Allowing his son to give up would force insure that his son never has any good memories. Second, the father's desire for his son to complete the journey speaks to the idea that every journey is meaningful. Regardless of a path ending in nothing, it is the journey to the end which matters the most.