This thought rousted me out of bed.
Ayn Rand pointed out that a corollary of Jesus' saying, "Judge not that ye be not judged," is "Judge and prepare to be judged." I think of this often and it occurred to me tonight that it's true psychologically as well. Your criticism of others reveals your own weaknesses to the psychologically astute.
I offer this infinitely copiable arrow to the intellectual quivers of the masses in this election season. It behooves us all to become psychologically astute - it's our best defense against manipulators...as well as it defends us from falling into the trap of being manipulators (which burns up our stock of good will, if you need to have the selfish, utilitarian argument spelled out).