It took me a while to realize why pride is the deadliest of sins.
It makes sense when you look at it from the perspective of the power of creation. If creation is the ultimate power from which all other power is derived, the worst thing that you can possibly do is assume that you are above it.
To believe that you are above the power of creation would mean that you would inevitably end up trying to destroy it in order to prove your superiority.
That road ends in the total destruction of everything entirely.