system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU] "I've ignored my destiny once, I cannot do it again. Even for you." What is Thanos referring to? When did he ignore his destiny?
gpt
Short answer: The more reasonable parties on Thanos' home-world didn't let him kill half the people there and he's salty about it.

Long answer: Thanos believes that his plan for universal genocide is the *only* solution to overpopulation. Overpopulation apparently ravaged his home world, which is when he initially had the idea to slaughter half the people there. Thanos' delusions manifest in such a way that he believes his culling is the most logical, rational plan. He believes that everyone else is ignoring his perfect logic, and that he is the only one with the will to act on what he sees as the only viable course of action, and thus it is his destiny. If you'd like to understand a bit better, you should look into narcissism and delusions of grandeur.