In some cases, looking at it from the perspective of someone outside of Catholicism, this might seem a bit unfair or if not unfair then somewhat unreasonable. Let us take two situations for an illustrative example of why some non-Catholics might consider this unreasonable:
Case 1: We have a mass murderer, someone who has robbed banks, tied up and tortured innocent people, killing them in painful ways. Someone who has caused enormous heartache and pain to many families. He blasphemes and curses everyone. He has used and has sold illict drugs ruining countless lives. He has kidnapped several young girls, ruthlessly raped them, and enslaved them in cages for years, not feeding them much, and one of the girls has starved to death. Finally, the police catch up with him and he is judged and found guilty on all counts and sentenced to die in the gas chamber. A short time before his execution, a priest visits him in his cell and he confesses his sins and further he does what is required to receive a plenary indulgence. He is then executed, but goes straight to heaven, as he has confessed, and has received a plenary indulgence.
Case2: We have a family man, a man with six children, working hard to support his family and at all times loyal and faithful to his wife and family. He goes to Mass several times a week, and always on Sunday, and says his morning and evening prayers. He gives as much as he can to the Church and to the many and various charities which request donations. He helps his wife around the house, doing the dishes, cooking various meals and cleaning up for the children and for his family. He brings flowers and other small presents to his wife and comments favorably on her hard work and how much everyone in the family appreciates her and loves her. He does not smoke, does not drink, and of course does not take any drugs except perhaps an aspirin once in a while to help with his headaches. He keeps the Church rules and he helps out with the cleaning at Church. Now one of his acquaintances at Church sees what a good person he is so he buys him a ticket to a local baseball game. The man accepts the ticket, even though the game occurs on a Sunday. He intended to go to Mass in the morning, but because of cleaning up the house and cooking some meals for his darling wife, he wakes up a bit later than usual and it is too late to go to Mass in the morning, so he goes directly to the ball game, intending to go to Mass later in the day, right after the ball game. However, at the ball game he meets an old friend and as they are reminiscing over various things, he agrees to go with him to the local Starbucks for a cup of coffee, realising that in doing so he will miss Mass and commit a mortal sin. They go to the local Starbucks, but on the way out of the restaurant, due to the fact that the man has been working so hard for his family and especially for his wife, the man has a heart attack and collapses and dies on the spot. So this man, then goes to hell, since he has committed a mortal sin of missing Mass on Sundays.
