I feel like that phrase is a little redundant. This statement is not quite as optimist as it sounds though. I think often times we say genuine person when we mean nice person. And the argument I want to make is that it is almost impossible not to be a genuine person. A deceitful person is being their “true self” by being deceitful whether or not other people know it.
Every action and every choice we make is based off our own experience, our own values, our own will, including how we choose to present ourselves. Some of our choices may be “out of character” at times, but even the things we regret had a rational behind it at the time (and whether or not something was learned says a lot).
If someone shows (not tells) you who they really are, listen.