Throughout history powerful leaders have paid the price for underestimating their opponents.
The first that we know of was Ravan. He thought Ram was just another guy in exile and look what happened to him. Even 10 heads were of no use.
There have been a succession of such guys in history, all over the world. For want of space, I will not list all of them here. Suffice it to say that it happens very regularly.
Indeed, it has happened all too often in India and those who make the mistake of underestimation go into complete oblivion. Yet no one learns.