The sin of Pride.
What is Pride?
“Now what you want to get clear is the Pride is essentially competitive – is competitive by its very nature – while the other vices are competitive only, so to speak, by accident. Pride gets no pleasure out of having something, only out of having more of it than the next man. We say that people are proud of being rich, or clever, or good-looking, but they are not. They are proud of being richer, or cleverer, or better looking than others.
If I am a proud man, then, as long as there is one man in the whole world more powerful, or richer, or cleverer than I, he is my rival and my enemy…it is Pride which has been the chief cause of misery in every nation and every family since the world began. Pride always means enmity – it is enmity. And not only enmity between man and man, but enmity between us and God.”
-C. S. Lewis