In this commentary on the paper by the Bank Street Reading and Literacy Alumnae Group, Korthagen states that, while it provides an excellent example of how fruitful professional development can be when it is grounded in the needs and strengths of the people involved; regretfully, many traditional approaches to professional development are based on a completely different assumption, namely that experts know what is important for teachers to learn. Korthagen suggests that a radical change of perspective is needed, and proposes a view of learning called "multi-level learning," which centers around the areas of personal needs and strengths. This view emphasizes that people who go through a process of deep learning change at several levels simultaneously. These levels, represented in the "onion model," are: (1) the environment; (2) behavior; (3) competencies; (4) beliefs; (5) professional identity; and (6) mission. Korthagen believes that when teachers become more in touch with their own identity and mission, this creates a change of perspective regarding the daily hassles of the profession and triggers fundamental growth that may lead to new types of behavior that are more in line with personal missions and inner potentials. (Contains 1 figure.)