I think the statement of "immovable body" needs some clarification. it seemed folks think that "immovable body" meant that one should just stand there to be stabbed. immovable body meant that if you (generic you versus you you versus yu which is a chinese guy selling those white buns of death in china somewhere) are very centered and capable of redirecting forces elsewhere and not moving if he/she/it so choose. and when he/she/it so choose to move, it will be an immovable body on rail, i.e. you moved with very centered. that he/she/it is very difficult being tip over/push over/pull over (unless he/she/it is drunk which will be pull over for DUI), generally not over of some form or fashion. so please folks, when you hear the phrase "immovable body" don't think that i will stand in one place and let you stab me. there is a different between capability and stupidity.
It was meant as a metaphor on the limitations of power Phi, not to be taken literally. You will admit that power has its limitations, won't you?