Mountain vs Faith Militant

Yes he did overestimate his power. He thought he had Cersei cornered into a position where she would have to show up to her trial and face further punishment. But like all her enemies to that point, he underestimated her ruthlessness.

Even if the High Sparrow was told about The Mountain, what could he do about it at that point? Send 50 more FM's to arrest the Mountain and Cersei??? Not only would the Mountain tear through them, but the rest of the Kingsguard would protect her too. If she showed up to her trail at the Septon then he would have her trapped and could have her arrested.

Didn't the High Sparrow only show up AFTER D&D ran out of GRRM book material and started making up their BULLSHIT?

Unless anyone can tell me that the High Sparrow and the Faith Militant are 100% George RR Martin inventions, I don't give a damn about them.

People like the High Sparrow aren't totally rational. They're so sure their deity has their back that they tend to miscalculate how events will turn out in real life, and they don't tend to rethink anything when things don't pan out, because they're sure the deity will do what they expect in a while. Plus their assurance that their deity worships *them* tends to lead to zero fear of consequences, threats have no effect on people who are looking forward to the glorious afterlife they expect.

It's really amazing that the Sparrows got as firm a hold on power as they did, but only an irrational person with no fear of consequences would even try the shit that got the Sparrow to the Sept of Baylor.