Hello. I've studied the golden rules of the feedback OP-AMP and applying this to voltage follower shows that voltage gain (Vout/Vin) is 1. Thus, Vout should eventually follows Vin when Vin suddenly changed. I've tried to follow this process for clear feeling by drawing pictures as shown in the attached image. Since AV is very large for typical OP-AMP, It looks Vout becomes divergent! (or becomes saturation value.) This divergence is even more clear when feedback equation is approximates to (V+ - V-)AVn where n is number of looping. (You can get this approximation by looking last shown Vout in the image.) What was I wrong? Why does feedback make the system crazy?