英語のことわざ

Trust is the mother of deceit

According to this proverb, once a person starts to trust you or to rely on you, it is easy to trick them or to take advantage of them. This proverb goes on to suggest that trust naturally turns into deceit, that is, lying to people and using them for your own purposes. So you should not trust people too much, you should not automatically think they are good people and they will not try to use you, because they will.