You are chosen to decide the 8th deadly sin - what do you choose?

You are summoned by an all powerful mystical being, who informs you that the 7 deadly sins are real in the sense that people who take part in them are slowly damned to an afterlife of hell/purgatory.

The mystical being deems you to be wise, and asks you to take your time, and decide what the 8th deadly sin should be.

This deadly sin will be taught among the human race, who will be cautioned against it, just as much as they are taught about the pitfalls of the other 7 deadly sins.

For those who do not heed this caution and continue to take part in it, their soul will slowly be damned.

What is the 8th deadly sin you choose, and why?