A psychologist is needed if you want to put your thoughts and feelings in order. For example, if you have trouble in a relationship with a partner. Or if you can't seem to "find yourself" and are annoyed with your job. Or if it seems that only bad things await you in the future - and this is alarming. In sessions with a therapist, you can talk about this, examine past experiences, identify negative thought patterns, and learn to respond to situations differently.
Sometimes, a client may not have a ready-made topic for a conversation with a therapist, but this conversation is needed for some reason. And sometimes, people who are going through a difficult divorce or the death of a loved one do not feel the need for therapy - and that is also normal.