assuming you are referring to the "personal experience interview" (PEI), it's in fact surprising that many candidates focus merely on preparing the case interview and underestimate the preparation required to master the PEI. The latter is a popular approach used at McKinsey to figure out whether the candidates personality matches the company.
To acquire a broad impression of the candidates' personality and the relevant aspects in consulting, you may be asked to describe experiences from your past which illustrate your ability to cope in the following three dimensions:
2. Personal Impact
How they'll approach these dimensions are up to their creativity. However, you can try to be well-prepared by gathering examples from your past that could prove each dimension authentically.