The Evil Eye
Hide yourself from public scrutiny, for their is nothing more destructive than the ayin hora (evil eye). The first luchos were accompanied by earth-shaking thunder, and therefore the ayin hora reigned and the luchos were shattered. The second time Hashem gave Moshe the luchos, He instructed Moshe to ascend Har Sinai discretely, along and without fanfare, therefore the luchos endured.
(Yalkut Shimoni 148)