The question is not new - in fact it is probably the original question (or maybe even the primordial) question. But her take on the response is interesting: Your answer should be 'big' enough to hold your life.
Do you define yourself as a cancer survivor? A father? A marketer? Are any of these answers 'big' enough to hold your whole life?
Suddenly we start needing multiple lables - and maybe that is a cop out? What is the 'lable' that will define who you really are?
And here is my little insight: Those who can define who they are most clearly and soonest, are the ones who become who they think they are best, and hence are the most successful? It is the philosophical equivalent of a USP or a brand proposition, or maybe even the sales equivalent of your 30 sec elevator pitch.
You don't only need it - but you need to live it. That is when the belief will manifest itself in your life.
Who are you?