Hereditary, storyline explanation below:

Rating: 7/10 (8 March 2019)

This movie is a horror masterpiece! Let me break it down for those who can't figure it out or find it hard to understand. I think this is a large part of the hate, because it can be a difficult story to wrap your head around:
Anne (the mother) states that one of her brothers starved himself to death, the other hung himself. She also says to her son (while sleepwalking) that she didn't want a son and tried to miscarry but couldn't.
The grandmother, had tried to put Paimon (one of the kings of hell) into her sons. But they would have rather died and did so.
Anne states that she would not let her mother near her son, as they were not speaking at the time. But out of guilt as her mother was getting older and senile, she let her nurse her daughter.
The grandmother took advantage of having access to her granddaughter and out of desperation put Paimon (the king of hell) into her gran daughter.
The grandmother caused the death of her granddaughter to then use her in the afterlife to get to her grandson. The fact that she is decapitated proves this theory, as her mother and father are also decapitated in the end. It is symbolic.
Her grandson is supposed to be the rightful air to Paimon. In the grandmothers books it states "Paimon must be in the body of a man to be strong"
Grandmother could only get to her grandson, after death. Using her satanic cult to do her bidding from beyond the grave.
Hope this helped. Watch it again and enjoy!