From the Shiur "No Bad in the world" by Rabbi Lazer Brody based on the teaching of Rabbi Shalom Arush

Ingratitude is heresy.

Often a person has one of 3 responses to problems:
1) They blame themselves
2) They blame someone else.
3) They blame "nature"

All 3 of these responses are heresy, because everything, even our problems, come from Hashem.