Rav Berg said, "There is nothing written in the stars that cannot be changed." This is because Kabbalah teaches that choices we have made in past lifetimes determined where we start out in this one, and our choices in this lifetime will determine where we end up. The decisions, therefore, are ours to make, and our fate is in our own hands. We come into this life to correct mistakes we made in past lives, and our soul chooses the exact time which offers us the best opportunity to: achieve what's called our Tikkun (or spiritual correction), to make different choices, and to overcome the limitations, which previously held back our soul's growth. Kabbalistic astrology would say, then, that our lives are not determined by the arrangement of planets, but that the arrangement of the planets is determined by our lives.
Each astrological sign has its own unique positive and negative attributes. As such, the signs we were born under are like a map pointing us to both our strengths and to what we came to correct. For example, those born under the sign of Leo have the incredible ability to influence many people, but need to be aware of coming from a place of ego, so that they can be a pure channel for the Light. And Geminis, who have the gift of wisdom, also tend to have trouble committing or following through. Someone born in the month of Gemini would know it is important to focus on sticking with something and seeing it all the way to the end.
When we understand this, we see that there are no "bad" aspects to our astrological charts, only different opportunities. Kabbalistic astrology allows us to be more aware of these opportunities, making it easier for us to achieve our correction, erase the negativity we created in the past, and become, essentially, the cause of our own fulfilment.