Trust is a fragile thing.
Two people share trust then one of them perceives an injustice and trust quickly comes into question. Whether the injury is 'real' or not, when the injury is perceived it is quite normal for the person who feels injured to retaliate...to seek revenge. Then trust is lost and anti-trust takes hold with a powerful appetite for growth.
The key to sustaining trust often sits at the point where one party perceives the other has done an unjust/unfair/unkind thing. At that point of recognition there is still opportunity to remedy the situation quickly and easily...at least relatively quickly and relatively easily.
When a perceived injury happens, the offending party may be oblivious. In many situations the real problem is the injured party has too-thin skin. Too-thin-skin and victim-thinking are common human frailties. These frailties are the consequence of lack of self-confidence. In other situations, the offending party may not be attentive or observant or empathic. Regardless of the reason, when one person perceives injury at the hands of another the offending party may be oblivious. The gap between of perceived injury and obliviousness is enough to fan the flames of distrust and revenge is, often, the natural conclusion. I say 'natural' because revenge isn't something reserved for the wicked and maladjusted. Revenge is in the genetic fabric of most human beings.
Revenge does not have to happen.
Revenge is like any other bad habit...it catches us, it gets repeated, it digs a deep habit-rut, then it owns us until the day we decide to work to overcome it.
The best way to overcome revenge is to recognise it is not deviant behaviour. It is a natural behaviour that doesn't work too well in our current society. And, it is something a person can control if that person wishes to control it. First, we must identify the breeding ground for revenge. Revenge comes to life when we perceive offensive behaviour in others. So, we can nip revenge in the bud if we stop and think during the 'I-feel-offended stage'.
We can be more trusting and cut the other person some slack. We can accept our self-biased tendencies. We can accept our tendencies to protect and bolster our own ego. We can choose to understand these tendencies cause us to over-react to other people's actions and cause us, regularly, to perceive offence where none exists. And knowing these things we can choose to ignore that little voice that tells us "That person just injured me." When we choose not to be injured revenge-thinking will not arrive.
As the saying goes, "You can act offensively but I don't have to feel offended." Even if another person is truly offensive, we do not have to feel offended. It is a choice. If we choose to not feel offended then revenge-thinking will not arrive.
Controlling egoic biases & refusing to be offended: we have these two ways to reduce/remove the need to feel revenge.
When we practice these two ways they become good habits, good habits that breed trust between us and other people.
Trust is a fragile thing - we can choose good habits that sustain & build it.