He said to his disciples, "Things that cause sin will inevitably occur, but woe to the person through whom they occur. It would be better for him if a millstone were put around his neck and he be thrown into the sea than for him to cause one of these little ones to sin. Be on your guard! If your brother sins, rebuke him; and if he repents, forgive him. And if he wrongs you seven times in one day and returns to you seven times saying, 'I am sorry,' you should forgive him." And the apostles said to the Lord, "Increase our faith." The Lord replied, "If you have faith the size of a mustard seed, you would say to (this) mulberry tree, 'Be uprooted and planted in the sea,' and it would obey you. (Lk 17:1-6)
Everyone sins in this world. There is no one on this earth who can say that he has not sinned (except Jesus Christ). There are sins which are caused by the others or external agents. These causes are also inevitable. There are persons, events, things which cause another to sin. However, one should be careful not to sin and much more, not to be a cause of sin. Sinner is forgiven (even is he sins seven times a day) but not the one who is the cause of sin.
Anyone who is the cause of sin for the other should be into the sea. He should be thrown with a millstone around his neck. This is so because not even his dead body should be seen (floating). Cause(r) of sin should not be seen. Jesus makes such a strong statement against the one who causes. Could this be because the little ones fall into sin because they are prompted to do so and not by themselves?
Sinner should be forgiven whenever he recognizes his sinfulness and repents. Jesus suggests that he be forgiven seven times (completely). Sinner will realize that he has sinned whereas the causer does not realize that he has caused the sin and hence he does not realize and hence the responsibility falls on the one who commits.
