You can decide for a non-violent protest yourself, but if you undertake it with a large crowd of people, sooner or later one of them will be provoked to violence anyway, the mood tips, the group dynamic kicks into action, the rest of the crowd is infected by aggression and the protest planned as non-violent usually fails.

Actually, it almost always works out that way, but Gandhi somehow made possible what cannot be possible according to the laws of logic, thus forcing the militarily stronger British to release India, who could no longer justify their violence to the population and lost face before the world.

I have no idea how he accomplished the seemingly impossible, which to this day almost all people fail at when they try, but the fact that he accomplished it shows what a special person he was and certainly a hero to whom first and foremost his people, but also many people outside India, pay great respect.