Complex sentence: Thus in the "Myth of Er", when the gods send all men to choose another life, the true characters of the falsely-pious and those whose are immodest in some way are revealed when they choose the lives of tyrants.
Split into simpler sentences: Thus in the "Myth of Er", the gods send the falsely-pious and those whose morals are out of conformity to norms to choose another life. The true characters of these are revealed when they choose the lives of tyrants.