And let my servant Lyman Wight beware, for Satan desireth to sift him as chaff. (D&C 52:12)
Gospeldoctrine.com has some little explanation about this that I thought useful to include:
"Chaff is the non-nutritious waste product of wheat and is separated from the grain by the wind when it is tossed into the air. This process is called sifting. Chaff is like a rudderless vessel that is driven at will by the wind. Satan desires to sift the Saints like chaff, to separate them from the soul-saving, nutritious grain of the gospel and carry them away in the winds of wickedness." (Hoyt W. Brewster, Jr., Doctrine and Covenants Encyclopedia [Salt Lake City: Bookcraft, 1988], 520.)
"[Lyman Wight] had been ordained a High Priest at the Conference and had received a vision. He was a most zealous and successful missionary. He was fearless as a lion in the defense of the Saints, and he was a terror to the enemy. At the April Conference, 1841, he was appointed an Apostle. But, notwithstanding all, there was a flaw in his character which the Lord saw, and of which He warned him in this Revelation. In April, 1844, he was tried before the High Council at Far West for teaching false doctrine. He acknowledged his fault then and was forgiven. But, after the martyrdom of the Prophet. he declared that he would not turn his hand over to be one of the Twelve, and when the Saints went to the Rocky Mountains, as the Prophet Joseph had predicted they would do, he and George Miller led a small company to Texas. Wight died in that State, March 31, 1858." (Hyrum M. Smith and Janne M. Sjodahl, Doctrine and Covenants Commentary [Salt Lake City: Deseret Book Co., 1978], 305.)
So back to this idea of chaff being like a rudderless vessel driven at will by the wind. There are two problems that can cause us to behave like chaff more than grain. 1) Rudderless- without using our agency to choose, we let others steer our lives. 2) Driven by the wind – without our own good purposes to drive us and motivate us, without the Lord’s purposes to bring about our immortality and eternal life, we are at the mercy of the purposes and drives of others and every wind of doctrine in society.
Furthermore, our faults in our character give Satan an opening to try to chisel us away from the Saints and the church. In Lyman Wight’s case, he seems to have been okay as long as Joseph Smith was alive, but once Joseph was dead, something in him balked at uniting with and working with the other apostles. He didn’t acknowledge their authority or see why he should unite with them.
We all have some particular weakness(es) that Satan will try to use to separate us from the church. We don’t have specific warnings addressed to us in the Doctrine and Covenants like Lyman Wight, but we do have patriarchal blessings, which usually have particular warnings in them. I have warnings in mine that I did not understand the need for until maybe 20 years after getting it.