In my reflections on Eastern and Western spiritual traditions, I always tend to converge the teachings by finding the commonality and bridging the difference. In this question, the first thing we need to do is to clarify the concept of the self. In many esoteric traditions, there are two selves: the Higher Self (which is also the Divine Self or Spirit in us) and the Lower Self (normally termed as ego). Apophatic spiritual traditions will always drive toward transcending the ego to be one with the Divine Spirit in us (the Atman or Dharmakaya) because the ego is just an illusion and impermanent, it is the higher soul (or Dharma body) that is eternal and permanent. Cataphatic spiritual traditions (such as Tantra and Ignatian spirituality) makes use of the ego to find God's presence in the present corporal reality.
Following the Tantra and Kabbalah traditions, I am inclined to see that the ego is an essential part of our human nature being a being within time and space. It is through our ego (our beliefs, thoughts, emotions) that we create our reality in space and time. The important thing is to purify the ego of negative programming from other people when we are growing up and to let the Higher Soul or Spirit manifest itself through the ego. The self is an essential part of being human but we need to let the self express our true nature and essence as being created in the image of God.
God loves us unconditionally so we have to learn to love our self. This is the reason why selfishness is something natural to being human. Kabbalah teaches that being creatures means that ingrained in us is the will to receive. God, the creator with the will to bestow, created us with the will to receive so we can receive pleasure from our creator. As I see it, selfishness is not the problem. The problem is how we define the self.
We normally define the self to be our body or our possessions. So we love ourselves and our possessions only to the exclusion of others. For parents with children, they sense and feel that their children is part of their selves. They naturally feel what their children feel because there is a sense of oneness among them. The parents identify with their children and feel their pain and joy. This reminds me of this saying of Jesus: Whatever you do to the least of my brothers, you do it unto me. I think that with Jesus' identifying with the least of the people, he becomes one with them in mind and heart. He feels what they feel and desire what they desire. To add to this, I have read of Hebrew saying that the true wording of the second commandment is this: Love your neighbor as your self. This wording emphasized that the neighbor is part of our self. When we see the neighbor as part of our self, then we feel what they feel and desire what they desire.
To summarize, the challenge for us is not to be selfless because it is going against our nature as a creation of God. Love of self and selfishness is natural and part of God's design. The challenge is really self-expansion. We need to begin to expand how we define our self - from our body and possessions to our kin, then expanded to include community and society, then expanded to include the whole world. The truth is that this is the ontological reality: the individual is part of the whole and the whole is part of the individual. What the individual does affect the whole but what happens to the whole also affects the individual. In Kabbalah, the concept of Adam ha Rishon states that our individual soul is just a piece broken from the original soul of Adam. When our consciousness have evolved from ego consciousness to collective consciousness (then to cosmic consciousness), we will begin to see that humanity and the earth is our self. With this expanded self, being selfish will mean taking care of others, humanity and the earth because when we take care of them, we are just taking care of ourselves.