If the Roman Catholic truly believes it is a "mortal" sin they will keep their priest right by their side to "receive their forgiveness" as it is clear people lie all the time.
...google the catholic difference between mortal sin and venial sin. You are referring to mortal but are describing venial. It’s well thought out actually and you will see that even should you disagree.
By which I mean "Baloney Sandwich."
I had an argument once with a Born Again preacher. He insisted there are no degrees of sin and the family who lied to the Nazis to shield Jews committed as great a sin as the Nazis who murdered them.
I contend that God never intended us to turn off our brains.
A Catholic does not need to keep a priest right by their side. From the Baltimore Catechism:
403. How can a person in mortal sin regain the state of grace before receiving the sacrament of Penance?
A person in mortal sin can regain the state of grace before receiving the sacrament of Penance by making an act of perfect contrition with the sincere purpose of going to confession.
404. What should we do if we have the misfortune to commit a mortal sin?
If we have the misfortune to commit a mortal sin, we should ask God’s pardon and grace at once, make an act of perfect contrition, and go to confession as soon as we can.
Illustrates the point that as pretty much everyone lies daily...and knowingly....the concept of the “mortal” sin is not a Biblical concept.
I don`t know for sure if mortal sin is a biblical concept or not but here is what is going to happen to liars.
Revelation 21:8
But as for the cowardly, the faithless, the detestable, as for murderers, the sexually immoral, sorcerers, idolaters, and all liars, their portion will be in the lake that burns with fire and sulfur, which is the second death.”