This is - how the GB try to explains this:
*** w81 12/1 p. 27 par. 2 The Path of the Righteous Does Keep Getting Brighter ***BUT - this is, what the bible says about "tacking":
2 However, it may have seemed to some as though that path has not always gone straight forward. At times explanations given by Jehovah’s visible organization have shown adjustments, seemingly to previous points of view. But this has not actually been the case. This might be compared to what is known in navigational circles as “tacking.” By maneuvering the sails the sailors can cause a ship to go from right to left, back and forth, but all the time making progress toward their destination in spite of contrary winds. And that goal in view for Jehovah’s servants is the “new heavens and a new earth” of God’s promise.—2 Pet. 3:13.
(Ephesians 4:14) in order that we should no longer be babes, tossed about as by waves and carried hither and thither by every wind of teaching by means of the trickery of men, by means of cunning in contriving error.
Or this WT:
*** w92 8/1 p. 17 How Are You Running in the Race for Life? ***
Run “Not Uncertainly”
16 Seeing the strenuous efforts needed to succeed in the race for life, Paul went on to say: “Therefore, the way I am running is not uncertainly; the way I am directing my blows is so as not to be striking the air.” (1 Corinthians 9:26) The word “uncertainly” literally means “unevidently” (Kingdom Interlinear), “unobserved, unmarked” (Lange’s Commentary). Hence, to run “not uncertainly” means that to every observer it should be very evident where the runner is heading. The Anchor Bible renders it “not on a zigzag course.” If you saw a set of footprints that meanders up and down the beach, circles around now and then, and even goes backward at times, you would hardly think the person was running at all, let alone that he had any idea where he was heading. But if you saw a set of footprints that form a long, straight line, each footprint ahead of the previous one and all evenly spaced, you would conclude that the footprints belong to one who knows exactly where he is going.
