Messages of hope aren't about keeping secrets.
To protect the earth and everyone on it, Kara must push herself in the Supergirl season one finale. She fights a mind-controlled Alex, she records a message of hope, and she prepares to sacrifice herself. Happily, that latter action wasn't necessary. She survives thanks to the assistance of J'onn and her sister. Their fight with Non and Indigo put them in contact with these secrets: