Alma 59

9 And now as Moroni had supposed that there should be men sent to the city of Nephihah, to the assistance of the people to maintain that city, and knowing that it was easier to keep the city from falling into the hands of the Lamanites than to retake it from them, he supposed that they would easily maintain that city.

I have heard people say that it is easier to ask for forgiveness than it is to ask for permission. I suppose that may work in business or in some other setting, but it isn't true in our lives in regard to sin. It is much easier to follow the commandments of God than it is to repent and right the wrongs in our lives. I was about to write that young people sometimes think that they will sin a little now and repent later. But that kind of thinking is not restricted to youth. In April 1993 General Conference, Elder M. Russell Ballard said the following: 

"You must be honest with yourself and remain true to the covenants you have made with God. Do not fall into the trap of thinking you can sin a little and it will not matter. Remember, “the Lord cannot look upon sin with the least degree of allowance.” (D&C 1:31.) . . . Some youth foolishly rationalize that it is “no big deal” to sin now because they can always repent later when they want to go to the temple or on a mission. Anyone who does that is breaking promises made to God both in the premortal life and in the waters of baptism. The idea of sinning a little is self-deception. Sin is sin! Sin weakens you spiritually, and it always places the sinner at eternal risk. Choosing to sin, even with the intent to repent, is simply turning away from God and violating covenants."