Question

why the non cooperation movement was failed?

Answer 1

The Non-Cooperation Movement failed because of the violence erupted in Chauri Chaura on February 5, 1922. 

Answer 2

The Non Cooperation Movement was called off by Mahatma Gandhi in February,1922 due to Chauri Chaura incident that took place in United Provinces in which 22 policemen were dead.In this incident, the angry mob had set the police station on fire.

After this incident, Mahatma Gandhi called off the movement as he thought that people of India were still not ready for a non violent movement.
He thought that this kind of incident could take place again and British government could easily suppress the movement.