If something turns off course or is diverted, it deviates from the expected or the norm. Deviating from explicit recipe directions is never a good idea, unless you want inedible food or a kitchen fire.
The verb deviate can refer to divergence from a predicted path or road ("the airplane's route deviated from the flight plan"), but it can also refer to a divergence from normal behavior or expectations. When women demanded the right to vote, their behavior was considered shocking and deviated from the expectations of the time.
