Warren Bennis, professor at the University of California and recognized expert on the subject of leadership says the following in his seminal book On Becoming A Leader:

Since self-knowledge is as Bennis said "the most difficult task any of us faces," and is a foundation to developing Emotional Intelligence, it is a critical element to include in leadership training. Through gaining knowledge of self through assessment and training, leaders discover and build on their own strengths, recognize that a strength done to excess can become a weakness, and begin developing a plan of action to address skill gaps.

The Myers-Briggs Type Indicator (MBTI)

Experts have long suggested that the beginning of leadership is to "know oneself." Unfortunately, this is easier said than done. It is often hard to take an objective look at oneself. That's where the MBTI can help. By filling out a simple questionnaire, the MBTI reliably sorts people into categories to which they already belong. Participants often comment that hearing the feedback is "like looking in a mirror." The MBTI puts words to what people have often suspected about themselves but lacked the language to describe.