Every brand has a brand personality. Not every brand chooses to manage that personality. That's a mistake.
Brand personality has been defined as the human characteristics that embody the brand or brand experience. Helpful? Didn't think so. Let's rethink this.
Brands can be fun, free willed, playful, studious, a work horse, etc. But those attributes don't drive much energy into the brand. Worse, your interpretation of "fun" may be decidedly different than mine. So we could work on the same brand using "fun" as the brand personality and end up in vastly different areas. I think that's an issue.
I recommend people start with analogies (cars, famous people, bands, etc.) and then unpack what makes them work for the brand.
You might start with mountain climber Reinhold Messner. But everyone might not recognize that name. Unpacking that might get you to: Courageous, personable mountain guide: skilled, knowledgeable, engaging, with an intense desire to help others succeed.
It can be short or long. Just help people get on the same page and visualize the potential so internal and external audiences connect with the same powerful personality.