Carl rogers asserts that an effective psychotherapist will

Create a non-threatening environment that enables the client to feel free to explore his/her own problems and find solutions for them.

Explanation:

Carl Rogers was one of the founders of the Humanist approach to Psychology, which is mostly known by its client-centered approach, which means that the therapist shouldn't have just one way to address human relationships, but instead, the therapist should adapt to the client needs. As each person is unique, so should be the therapist approach, always considering what will be more effective to the learning/therapy process.