Korach is a classic example of a person with great potential, who made wrong decisions. The Sages tell us that Korach was a wise man. He was chosen to be one of the select few who were spiritually fitting to carry the Ark of the Covenant. 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 Moses and Aaron themselves were from the Tribe of Levi.
And yet, Korach starts up a dispute with Moses, and ends up being swallowed by the earth. What went wrong?
Actually, the question itself is wrong. Nothing "went" wrong. Korach had free will and he "chose" wrong. There is no determinism. Korach was not caught up in a wave of events over which he had no control. Korach 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. Korach's arrogance made him feel that he was not given enough honor, and he made another choice to enter into a dispute with Moses. From beginning to end, he was choosing.
This week's Torah portion begins with the word vayikach, "and he took." Korach 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. Korach 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 the Almighty's help, through our own efforts and our own choices.