Actually, I know of an example even more extreme than Malcolm's. A student about to graduate from Princeton Seminary decided to enroll in medical school. When an astonished professor asked him why he made this atypical choice, he replied that after considering all the alternatives, he found medical work the least appealing. He concluded, then, that this must be the profession God wanted him to enter. It's not hard to understand how Malcolm and the seminary graduate reached their conclusions about God's will.
Scripture has plenty to say about the dangers of trusting our gut instincts.
Perhaps the most notorious biblical example of the heart's deceit is David's attraction to Bathsheba. David was so devoted to the Lord that he is held up throughout Scripture as the ideal of a godly person. Yet he not only committed adultery but murder because of his enchantment with this woman. I suspect that David may well have rationalized his actions as being in God's will. Since his feelings for Bathsheba were so strong, he may have thought that God was prompting him through them to do something which he never would have considered in a less-crazed moment.