How does one do this? Where does one even start?
I believe it starts with recognizing where the lack of trust stemmed from in the first place. Often people avoid thinking about things that cause them pain (ignoring or minimizing the impact or the opposite extreme - becoming bitter or phobic about it because it becomes built up in their head bigger and bigger).
Often when those things that have undermined trust happened, the person was vulnerable and felt very powerless. Therefore, by recognizing the full impact of what happened, and bit by bit allowing oneself to look at it, it can get shrunk down to a manageable size and better responses can be chosen. (Long after a person is dead and gone, their words/actions are still impacting the people they affected negatively. Recognizing the factors that made someone act as they did doesn't excuse their actions, but it does make them more human and take away a lot of their godlike power in one's head. The key is for the person to realize that they have more power than they actually believe they do and therefore are capable of dealing with what happened in a proactive way). It is not that the unkind person is always a bad person, but rather that they have unconsciously chosen to protect themselves from ever feeling that vulnerable and powerless again.
When we follow a course of action or thinking that isn't working for us and we get stuck in it, it creates extreme frustration, which boils over into aggression. When we are able to get "unstuck", then we are free to try new courses of action or thinking that will yield better results.
To do that, the person must actually look at what isn't working for them, which means going back to the original problem. It requires coming to a place of futility where the person recognizes that what happened was wrong but that they can do nothing to change the past. What they do have control over is how they let that event or that person continue to impact their present or future and also whether their experience can cripple them, or positively impact others by how they respond to it.
By grieving over it, and then getting to a point where they start following a new course of action that will work better for them, they can develop resilience, and they can become proactive in their own situation. You can't change the set of circumstances you were given, but you can change your reaction to them.
For a lot of people, it helps them to have someone to talk to about it. For most, they need to develop trust again with someone (preferably in a non-romantic context, as that introduces a whole other layer of complications) and recognize that the responses they adopted in reaction to the original situation are no longer necessary here. At first, it may be easier to begin by learning to love a pet, as it is less vulnerable than loving a person.
This can be done, but it is usually a process of months or years and it requires willingness to go in and deal with something that is very scary. The longer it has been avoided, the more difficult it is to face. In the end, it often is more of a relief than a terrible ordeal to face it, but it feels like the Monster At the End of the Book before that happens. The fear that is there is not a rational one, but it is a very real one.
