Every day I have an in depth talk about life lessons with my friends.
Yesterday was integrity, about how doing the right thing, even when no one is looking, is vital to a happy life and building good character. About how lying once creates more lies, and how it might be not pleasant or even downright painful to tell the truth in the moment, but that is will net a beneficial result overall. (Of course if the Nazis come to get Anne Frank you can lie about that to save an innocent life, but that is an extreme rare scenario and shouldn't be considered a real option unless something dire happens)
What also comes with integrity is doing what you say you'll do. If you tell someone you'll be somewhere at a certain time, do it. If you tell someone you'll take care of something, do it.
...that only through integrity can we become our very best selves.