Sometimes you have to treat the symptoms so you can get the person functional enough to then start treating the root cause. For example, this is the point of anti-depressants and fever-reducing medication. They don't treat the underlying disease. They just keep the symptoms from killing the patient long enough to do something about the disease.

A person with particularly bad PTSD may not want to see a therapist and start rooting around in those bad memories. If the overall anxiety level associated with those memories can be reduced, then maybe the therapy can start.