Saturn mahadasa need not always be bad for anyone. It depends on how potent the planet is, whether it is inclined to do more good or bad, the residential strength of planets etc. The career is determined by the 10th house and the potency of the house. Read my blog navagrahastro.blogspot.in patiently and you will have a better knowledge about the scope of astrology in life.
Same is the case with Sade Sati too. If Saturn is good in the horoscope you will have a smooth sailing. Otherwise life will be miserable.