As a Mormon, I associated sin with breaking the rules of the church, going against the words of the prophet, or failing to do what was expected of me as a member. For example, I never was a smoker, but I knew an older man who was and he struggled over continuing to smoke because it was against the Word of Wisdom. He still came to church, and even served in a voluntary position as the ward clerk, but he smoked in secret. I knew this because as a missionary in his ward, I ran into him after church one day in the street. He flipped his cigarette over and somehow put it out in his own hand before my companion and I arrived at his side. My companion and I had heard rumors and then we saw him in the act. But we didn't say anything about it to him because we'd heard his wife was ashamed of it and we didn't want to make it worse and have him go inactive.
As for me, I felt worried if I skipped going to sacrament meeting and taking the sacrament because that was considered to be a necessary "renewal of my baptismal covenant" with God. (One of the LDS apostles, David Bednar, said this: "Through the ordinance of the sacrament we renew our baptismal covenant and can receive and retain a remission of our sins.") I was fearful if I didn't pay my tithing because I didn't want to "burn" when the Lord came again to the Earth. (He that is tithed shall not be burned at his coming: D&C 64:23) Once I refused a calling and felt guilty for that because I'd been taught callings came from God, and refusing a calling was refusing to serve God. Various church leaders and prophets said that members should not watch R-rated movies, so I felt wicked for giving into temptation and seeing "Schindler's List." Not getting visiting teaching done, not going regularly to the temple, not treating garments (underwear for people who have been "endowed" at the temple) with proper respect (seriously--don't drop them on on the floor, don't let people see them, don't roll them up to wear more revealing clothing over top, wear them 24/7) ("How it is worn is an outward expression of an inward commitment to follow the Savior," First Presidency Letter, 10 Oct. 1988)....there are many ways for a Mormon to "sin" besides breaking the Ten Commandments. Now perhaps I missed something in all those 27 years of being a member and am classifying all this as sin for Mormons when perhaps another member of the church would say sins are only things like being unchaste, lying, murdering. Let me look up how they define it on their official church website.
Sin: See also Abominable, Abomination; Filth, Filthiness; Offend; Rebellion; Ungodly; Unrighteous, Unrighteousness; Wicked, Wickedness
Willful disobedience to God’s commandments.
So now I ask, what do they consider to be God's commandments?
Commandments of God: See also Commandments, the Ten; Law; Obedience, Obedient, Obey; Sin; Word of God
The laws and requirements that God gives to mankind, either individually or collectively.
Remember the man I saw smoking? Well, the Word of Wisdom is considered to be a commandment currently, although it was originally "given as a principle with a promise." If a person uses tobacco, drinks tea, coffee, or alcohol or uses illegal drugs, they are not allowed to attend the temple.
There's the "law of chastity"--no sexual relations before marriage. Breaking that can get a person as far as excommunicated depending on how much happened and if the person has been "endowed" in the temple.
Here are a couple more things (found under under the definition for Obedience):
In nothing does man offend God, save those who confess not his hand and obey not his commandments: Doctrine&Covenants 59:21
I the Lord am bound when you do what I say: D&C 82:10
When we obtain any blessing from God, it is by obedience to that law upon which it is predicated: D&C 130:21
People must be chastened until they learn obedience: D&C 105:6
Can you see why Mormons run around stressed out, doing everything they believe is expected of them? It isn't just the peer pressure they put on each other to conform. They think they have to earn blessings, contribute to their salvation, prove themselves to God. I feel so sorry for them.