Some divrei torah are not very fashinable. This is one of them. The psukim and Rashi make it clear what the cause of man’s first sin was. HaShem told Adam not to eat from the tree, but Adam added a command to Chavah – telling her not to even touch the tree. But Adam did not reveal to Chavah that this was his own addition; he presented it as if the no touching was HaShem’s Command. Therefore, when the serpent pushed Chavah against the tree and Chavah did not die, she thought there’s also no problem to eat the forbidden fruit, and she sinned and caused Adam to eat and sin too. The lesson here is to clearly differentiate between halacha and chumra, ie what is halachically forbidden and permitted and then clearly demark what have been added as chumras and to realise that they are chumras over the halacha, and not confuse them with the halacha itself.