Ahithophel became an advisor for Absalom and his advice was not viewed as whimsical. "The advice of Ahithophel, which he gave in those days, was as if one inquired of the word of God; so was all the advice of Ahithophel regarded by both David and Absalom" (2 Sam 16:23).

But Ahithophel made a big mistake. He found his identity, his sense of purpose, in his counsel. It became his god. In fact, it was so huge, that when Ahithophel's advice was not followed, "he saddled his donkey and arose and went to his home, to his city, and set his house in order, and strangled himself" (2 Sam 17:23). 

Clearly, this guy had issues. Someone doesn't listen to his advice so he hangs himself over it? If parents did this every time their teenage kid didn't take their advice we'd have no adults left on planet earth.

Ahithophel's action is extreme because his whole life is wrapped up in Mr. Idol named counsel. Any time we find more satisfaction in the created than the Creator, we make the same error and its consequences can be fatal.