They were betrayed before
Some people develop trust issues after being betrayed by a lover or friend.
Due to their upbringing
Some parents raise their children to not trust any person easily, which leads to serious trust issues when they get older.
They fear betrayal
Some people have a natural fear of being betrayed, which prevents them from trusting any person easily.
They are introverts
Introverts usually do not open up to people easily. They take their time to know a person first before they can trust them. (See The body language of introverts)
Hearing about bad experiences
Some people develop trust issues when they hear from the people around them about bad experiences that they went through related to trusting someone.
Due to a troubled childhood
Experiencing a troubled childhood is one of the most important factors leading to trust issues.
They fear intimacy and closeness
Some people have a fear of being intimate or close to someone, as they believe it might never last. This can lead to trust issues as well. (See Why some people fear intimacy?)
Knowing someone’s past
Often in relationships when a woman knows her partner had cheated on someone before, for example, she will not easily trust this partner.
They fear rejection
Some people develop trust issues as a result of their fear of rejection. Therefore, they choose to not put themselves in any situation that may lead to rejection.
They are paranoid
Some people are paranoid, which means they believe people want to hurt them in some way regardless of their true intentions.
They are antisocial
Antisocial people usually do not trust people easily as a result of their lack of social interactions.
They have insecurities
People who have insecurities often find it hard to trust other people, especially if what they say or do contradicts their self-image.
Why some people have trust issues?
Trust Issues: Why Is It So Hard for Some People to Trust? What does it mean for someone to have trust issues?