It depends. As astrologers, we know that some people, with a mutable emphasis in their birth charts, have more changeable personalities, while others (say, with a significant Uranus or Pluto in their horoscopes) have charts that suggest dramatic change over the course of their lives. Still, psychologists have been arguing about the question for decades.
In the 1960s, the world of psychology accepted the fact that personality was stable – that we can be categorized as certain types of people and will consistently behave in particular ways. Yet when Walter Mischel, PhD began his professional career, he reviewed the literature and saw that none of the studies he consulted supported that conclusion. Instead, in his 1968 book, Personality and Assessment, he revealed that personality is not stable over time. Consistency was an illusion. Despite the research behind the book, it was controversial. People just didn’t want to accept that personality was unstable. On a gut level, we want to believe that we know who people are and can predict their behavior.
What Mischel also found, and others have supported, is that the different situations that we find ourselves in can very much change behavior. One may have one type of personality at work and another at home. And certainly, people change over time. An alcoholic can recover, a criminal may rehabilitate himself, a 30-year marriage can dissolve when the parties develop differing goals.
With astrology, we see why all of these variables are possible. The birth chart is stable – we live with that pattern throughout our lives. But we also experience different cycles and phases as we move through the years and decades. Progressions will change our personal emphasis in life, and transits will alter what the world is showing us. So in some sense, we are both consistent and changeable. And astrologers also have the extraordinary ability to forecast these trends.