In rotary mode, the drill string rotates continuously and delivers predictable ROP. In sliding mode, rotation stops, the BHA is oriented to steer the well, and the bit advances without string rotation. That shift solves the directional problem and creates an operational one.
Without string rotation, friction between the drill string and the wellbore wall increases significantly. Weight-on-bit transmission becomes less efficient, and the tool face is subject to constant torque-reactive movement as the bit encounters formation changes, stick-slip events, and varying WOB. Slide drilling ROP drops compared to rotary mode, and every manual correction the driller makes to chase tool face introduces variability into the directional outcome.
Tool face control drilling in sliding mode is not a skill problem. It is a physics problem. The string is long, surface control inputs are delayed by string length and torque transmission mechanics, and feedback from downhole is slow relative to the rate at which the tool face can move. Manual correction is always chasing a moving target.