As human beings, we trust our own judgment to help us decide what to do and who to trust. If our instincts fail to inform us and we or a loved one ends up being hurt, we blame ourselves. A character who has experienced this can easily develop a fear that their instincts are faulty, they'll let them down again, and they shouldn't be trusted.

Needing hard evidence to trust someone; not relying on discernment or inference
Doing in-depth research before making decisions
Writing off hunches without fully considering them
Seeking advice from others
Relying on others to make decisions for the character
Starting from a point of distrust when confronted with new people or situations
Resistance to change
Not pivoting quickly; needing time to adjust to new situations
The character changing their mind once a decision has been made
Avoiding or postponing decision-making
Being risk-averse
The character blaming themselves when things go wrong
Alternatively, the character always blaming others so it's not their fault when bad things happen
The character hedging their bets by responding with vague or ambiguous answers 
Indecisiveness or being wishy-washy
The character putting on a front of apathy or carelessness so they won't be expected to make important decisions or care if things go south
Expecting the worst from people so the character won't be disappointed or surprised