Why were stalin's five year plans unsuccessful?

It was a failure because the quotas set by the government was idealistic.  Given the time frame, its goals to achieve industrialization would take more than just five years.  It would actually take decades to attain that goal.  It would require time to train people to get to that level if industrialization.  Apart from that, their program of collective farming would produce more crops and subsidize other programs and projects had opposite effect.  It only led to the disruption of the food supply and caused famine in the country.