The last chapter of Kaling's book provides perhaps the best insight, and is the most down-to-earth. She talks about how her confidence comes from entitlement, which comes from working hard, and how working hard is actually ok, despite what many people think.
She also talks about people hating her because she thinks she's so great. As she says: "It's not that I think I'm great. I just don't hate myself...And the scary thing I have noticed is that some people really feel uncomfortable around women who don't hate themselves."
In the same chapter she talks about how telling girls alone how difficult it is to be confident implies that girls won't be able to do it. Which is obviously bullshit.
This whole last section was so poignant and well put, it makes the purchase of the book worth it, no matter what your feelings are towards the first half (which I also enjoyed, so bonus for me).
I'll leave you with one more piece of advice from Ms Kaling: "work hard, know your shit, show your shit, and then feel entitled". Preach it girl.