Should you always trust others? Of course not. Some people behave in very untrustworthy ways, and you should not make yourself vulnerable to them. You need to be able to tell when it is appropriate to be trusting and when it is not. You must develop the capacity to size up situations and make an enlightened decision about when, whom, and how much to trust. Remember not to reveal yourself so fast to another person that he or she is overpowered and bewildered. Remember, too, there are situations in which trust is inappropriate and destructive to your interests.
Never trusting and always trusting are inappropriate. Trust is appropriate only when you are relatively confident that the other person will behave in such a way that you will benefit rather than be harmed by your risk, or when you are relatively sure the other person will not exploit your vulnerability. In some situations, such a competitive ones, trust is not appropriate. When you have a mean, vicious, hostile boss who has taken advantage of your openness in the past, it is inappropriate to engage in trusting behavior in the present.
David W. Johnson (2014) Reaching Out: Interpersonal Effectiveness and Self-actualization. Boston: Pearson. P.105.