Korah is a classic example of a person with great potential, who made wrong decisions. Our Rabbis tell us that Korah was a wise man. He was chosen to be one of the select few who were spiritually fitting to carry the Aron Hakodesh. The Zohar tells us that of all the Tribe of Levi, he was the one with the greatest potential. That's pretty high praise, especially when we remember that Moshe and Aaron themselves were from the Tribe of Levi.
And yet, Korah starts up a dispute with Moshe, and ends up being swallowed by the earth. What went wrong?
Actually, the question itself is wrong. Nothing "went" wrong. Korah had free will and he "chose" wrong. There is no determinism. Korah was not caught up in a wave of events over which he had no control. Korah made some very bad decisions. He became incredibly wealthy, but the wealth led him to arrogance. It's common for that to happen, but it was still a choice. Korah's arrogance made him feel that he was not given enough honor, and he made another choice to enter into a dispute with Moshe. From beginning to end, he was choosing.
The Perasha begins with the word vayikah, "and he took." Korah took that which was not his. He "took" it - actively and consciously.
Shakespeare is wrong when he says "some are born great" and "some have greatness thrust upon them." People only "achieve greatness" through their choices. Greatness through birth, and greatness thrust upon a person, are only greatness in potential. True greatness must be achieved. Korah was great in potential. But he chose wrong and had only himself to blame.
The same is true of all of us. When we do not achieve the spiritual and moral heights we may aspire to, we can blame circumstance; we can blame upbringing; we can blame nature. Ultimately, though, we are responsible for our own choices. And conversely, when and if we achieve greatness, it is ours and ours alone - because we will only have "achieved" it, with Hashem’s help, through our own efforts and our own choices.
Rabbi Isaac Farhi