Do you ever see a Christian doing something that's spiritually damaging to themselves and others, but saying anything seems tough? Often it's honestly easier to just leave your brother or sister alone and not go through confrontation, because it'll all come out in the wash, anyway, right?
Although it's tough to hear, such inaction is one of the reasons Israel fell. "His watchmen are blind, they are all ignorant; they are all dumb dogs, they cannot bark; sleeping, lying down, loving to slumber." (Is 56:10) Often we fear the unknown, and the conflict inherent with addressing sin has unknown outcomes: will he/she hate me? Will I be loving enough? What would I want for me?
REMEMBER, even though it's tough, "He who turns a sinner from the error of his way will save his soul from death and will cover a multitude of sins." Make sure your motives are love and kindness, not just condemnation and outrage, because "the kindness of God leads you to repentance." (James 5:20; Rom 2:4)