Many shadows are formed early in life by ourselves rejecting aspects of our own character. The reason these aspects of personality are rejected may go back to early childhood. When we're young, we depend on main caregivers for everything. As a result, we become very attached to them and their way of doing things.
For example, if a caretaker disciplines a young child for being outspoken, there's a chance that as a young child, that person won't feel safe speaking their mind from that point on, even as they get older or even as an adult. That message becomes internalized, buried within the subconscious, and can therefore become an emotional activator for seemingly no reason.
In the example, if one's shadows is around speaking their mind or truth, it might bother one to see other people doing so. Every time somebody is outspoken, it might bring up unexplainable feelings of anger and resentment since believing that speaking up is not a safe thing to be doing.
One way that this type of shadow can be discovered is through writing down answers to related questions and exploring the memories, feelings, emotions, etc. that are brought to the surface while doing so.