Memory is something important to humans. Memory is something that shapes a human into a person. A person's personality can even be different depending on the memories they have.
Memory is part of a human. Memory is the past that has already passed. Memory is something that cannot be changed. Memory is something that is eternal. Memory has no physical form. Memory is created by passing through the past and continuing towards the future.
However, a person's memory can disappear because of something trivial. Accidents or minor head injuries can affect memory depending on the severity of the accident.
But what about someone whose memory changes? Can a memory change?
Of course not, because memory is something that is fixed. Because memory comes from past memories that have already passed.
That's why William is crying now, he realizes that Maria's memory is not something that has changed now, but the world itself has changed.