Because you are worthy of your own love irrespective of whether your love is reciprocated by another or not. You are the embodiment of love foremost. If you wait for another person to love you back, you are bound to suffer because at some point, someone will disappoint you. But if you love yourself first and you fall in love with another person and the relationship ends, what is left is still your love for yourself which should be there all along. All the best!