One should never trust a person unworthy of trust. Nor should one blindly trust a person deserving of trust. One should always try to secure other's confidence. One should not, however, himself trust his foes.
न विश्वसेदविश्वस्ते विश्वस्ते नातिविश्वसेत्॥ नित्यं विश्वासयेदन्यान् परेषां तु न विश्वसेत्।