Because he's so focused on having this desire become reality, he completely disregards his son's desires for his own life, and his son ends up killing himself because he sees no hope for a future that he desires. But it goes further than that. The father's desire obviously isn't just that his son become a doctor. The father also desires to be proud of his son, but on his own terms. He also desires to be in control, and seeing his son do things that he hasn't sanctioned, such as act in a play or be on the yearbook staff, takes away much of that control, and he can't stand the idea of losing it.
People also have problems when they desire things that are inaccessible.
Advertising plays a large part in this problem, for advertising exists to a large extent to create desire in an audience. The desire for an object has added stress and strain to a life, and to the lives of that person's family members. I married very late, and for a very long time, I desired nothing more than to be married. Because of this desire, I often approached relationships in a very forced way, a very unsure way. I hardly allowed myself to be myself, always trying to fit some role, even though I was trying to be myself.