The whole foundation of humanity is based on love and affection for each other, especially within blood relations. Human kid is the only kid that requires 12 + years of unconditional nurturing (by parents) to reach the stage of independence. Even after that, in any normal family, mom and dad are ready to do anything to to save the kids from any pain. Just assume of a situation where an evil person points a gun at your family and demands for at least one life. I am sure that most of the parents will give theirs happily to save the kids.
But on the day of judgement, we are told that moms will throw their babies away and run, and everyone will only be worried about themselves. This concept always bothered me. How can a mother enter paradise knowing that her kid is going to the other place? Even if she is forced to enter the paradise, will she be happy? However we are told that Jannat will be the place of eternal happiness.
Now lets assume that sadness really would not exist, and that mother would not be sad. Then that mother would not be the same person. She would be a (for the lack of better term) a brainwashed being, cause a normal person would not be a happy person knowing that her kid is burning in hell fire. So in reality, its not you but a brainwashed creature is going to enter the jannat on your behalf!!
Did my confusion make sense to you? Do you think like that too?