First, it's important to know that, in general, psychotherapy is highly effective. Across a wide range of psychological problems and many different types of people, therapy simply works.
For some, the benefits of therapy can be obtained in as few as seven sessions, while others need more to improve. Considering that many untreated problems last for years, or even a lifetime, psychotherapy can be life-changing.
If the particular therapist and type of therapy received are not as important as we thought, who or what does influence outcome?
To a large extent it's the client. The quality of a patient's participation in therapy is a key determinant of the outcome.
Understanding how clients make therapy work requires a drastic overhaul of the assumption that they passively respond to the ministrations of guru-like therapists. On the contrary, it is clients' active participation in therapy through their involvement, learning and application of what they learn that leads to improvement.
For this to occur, it helps if clients are open to exploring their emotions and internal experiences and are willing to endure discomfort and make efforts to achieve change. This requires motivation; enhancing motivation prior to therapy improves outcomes.
Perhaps this is why clients who are in greater distress at the outset of treatment tend to show greater benefit.
Therapist as dance partner
Clients undergoing in-person therapy don't do this work on their own but in collaboration with their therapist. The quality of this collaborative relationship is in itself an enormously important contributor to good therapy outcomes.
In a good collaboration, both therapist and client work at maintaining a positive relationship and need to continuously respond and adjust to the other, much like dance partners working in synchrony do.
As it turns out, good therapists (I said I'd come back to this) are attentive to building just such a positive alliance and repairing it as needed. They are good at being responsive to clients' evolving needs and wishes in treatment.
Finding a good therapist then becomes a matter of finding someone who listens well, empathizes, is responsive and can empower the client with hope and bravery to do the difficult work ahead.