All there is to it

Somewhere I heard someone say that you have to love yourself first before you can love anyone else or expect anyone else to love you. That sort of became my motto. I just can't help but wonder now, how come my friend, who has way more and difficult problems than I have, can love and have a relationship with somebody else? What is it that she can that I can't? I know she doesn't really love herself. Yet she is capable of loving and being in a healthy relationship with somebody else.
So is the 'loving yourself first' stuff just bullshit? Did I hold on to that because learning to love myself is less scary than loving someone else? Did I just push the problem away by making up other problems?
I fucked up before. Does that mean I will fuck up again?