Something you learn when teaching is that most people do not remember most of what they hear. Even when someone appears to understand, even when they're able to apply what they've just learned and solve problems correctly, they will most likely forget. Often a week later they have little to no memory of it. I've often been told by a student that this is the first time they're hearing something I told them the week before. It isn't my memory versus theirs; I have notes as well.

You should factor this in when you call people insensitive or mean for not understanding your life or the struggles you face.

You should also factor this in when people tell you about things they face. In all likeliness, you will not understand or remember much of what they tell you unless you make specific efforts.