Some of the basic choices you have to make when doing the - what should be rare but seems to happen whenever a new brand manager comes in- task of defining a brand focus on a choice.
Build the brand on:
Why you exist
What you do
How you are
Where you want to go
All have some level of merit, perhaps with the exception of 'how you are'.
Tone of voice, personality traits are massively important and often overlooked when it come to building communications, but are flimsy to build a brand on.
Because there are not many personality traits to around.
For example, as has been said elsewhere, umpteen agencies like to talk about how they are curious. Not only is this as generic as soft drinks saying they're fizzy, or trainers having cushioning, it doesn't instanty create a picture of why you're better, just how you go about things.
Now consider the teachings of Saint Byron Sharp.
Brands don't need to be different, just distinctive. They need to get noticed.
Just Do It wasn't powerful because people thought 'oh they'll empower me' it was utterly fresh and provocative.
As was 'the future's bright' which, I'll wager, the average mobile phone buyer didn't understand, they just liked how it made them feel.
The most reliable way I know to do this is have a point of view on something that matters.
It has to be relevant to product/brand of course, but for example, Guiness and 'Here's to waiting' wasn't successful because it focused on a feature of the experience, it freed up an utterly distinctive point of view on the world and some of the best advertising ever...in a relevant manner.
I guess that means if you have a starting point, it's a mixture of 'why you exist' and 'where you want to be' but personally, a great point of view seems to convey so much more, especially if it starts by relieving some sort of tension in real life you can credibly get involved in.