Charles Spurgeon once said, “Discernment is not knowing the difference between right and wrong. It is knowing the difference between right and almost right.”
Biblical discernment is sorely lacking today, because there is a lack of biblical knowledge. Often, study of the Scriptures has sadly been replaced by "how-to" seminars and feel-good books. When human opinion replaces God's Word, the result can only be a mess.
For a thoroughly biblical, yet brief, treatment of this subject, go to "The Watchman's Bagpipes," here.