A short-lived series of private lessons took place after Christmas in Harry Potter's fifth school year, during which Severus Snape attempted to teach Harry the skill of Occlumency. The lessons were finally cancelled when Harry was caught prying into Snape's memories, discovering the strangest things: there was a Prophecy about him, his dad was a bully, and Severus Snape had been in love with Harry's mum. Naturally, Harry now has a million questions. Snape would prefer to answer none.
The world is full of obvious things which nobody by any chance ever observes. The same question rises in every soul: “For what, for whom, must I kill and be killed?”
…Or, a classic approach to stubbornness.