There are only two times in your life when you need to let a person go from your existence: when you no longer have the ability to appreciate each other, or when you no longer trust each other. Trust is the foundation of every single positive relationship in the world. Without it, the relationship will not be able to be positive. If there is no trust on day one, do not count on there being any on day 1000.

A person may trust no one in their life, or they may trust only certain people. They may not even be aware of why all of their relationships seem so difficult, not ever realizing it is because of no trust. 

When you do not trust, you never take people's statements at face value. Your mind immediately takes their statements and rearranges them into what it thinks they actually mean. This leads to accusations, drama, pain, and bad relationships. 

So why would someone consciously or subconsciously decide not to trust? 

They believe that by not trusting, they are somehow protecting themselves. They may have been fooled once by a person breaking their trust, and the pain was terrible. Instead of realizing that it was just that person, they allowed that experience to put up a wall, and affect the way they view the world. 

If you are mistrusting, you will repel people who are trustworthy. No one likes to be accused of things they did not think or do, and no one likes to have to defend themselves when they did nothing wrong. 

Trust does involve being vulnerable. Yes, if you again misplace your trust, someone could take advantage of it, and you could get hurt again. But if you choose to not trust anyone, though you will never get fooled, you will also live in a constant state of anxiety, paranoia, and cause pain to people because you were unable to move past a bad experience with trust. The pain from a lifelong experience like that far outweighs the pain of getting fooled a couple more times.

When we are young, we are all naive. Naive people get hurt by trusting. From there, they can choose to either become experienced, or bitter. No one can make that choice for them, but it is a choice that will impact all of their relationships for the rest of their lives. It is a stronger choice to trust again, and you will be fulfilled much more than you will be fooled by choosing it.