This question reminded me of a very old joke that goes like this:
"How many psychiatrists does it take to change a light bulb?"
"Three, but the light bulb has really got to want to change."
In the answer, lies the whole crux of the matter. For any change to occur, the person, him or herself, must want to make it happen. If they have a deep desire or pressing need, then yes, people really can change the way they are.
There are so many different facets and varieties of change, almost as many as there are human beings. We could be speaking of physical, psychological, environmental or even economic change, to mention just a few. But with all of them, we make the assumption that this change we seek is for the better. Why else would we even consider it?
To illustrate how human beings can really change, a few real-life examples might promote understanding of the concept and the argument for the "yes" response to the question. Take the person who has always put the needs of others before their own. This caring behavior has, by the time they reach mid-30s or 40, become ingrained as part of their personality, a way of life. Till suddenly it dawns on them that they always do the giving and everyone else takes. It might be difficult to change the habits and beliefs of a lifetime. Yet a little more self-concern and awareness would enable that person to make positive changes - the kind that will allow them to ask for what THEY want, to take more help. Because once they reach that stage of enlightenment, if nothing is done to alter matters, resentment and hurts will build up. The motivation for change is therefore strong, and that person really can change their life to their advantage.
What about the person who has been so busy working and getting by, that they forget to look after their health properly? The wake-up call could be a heart attack or high blood pressure, certainly something life-threatening. This means that their whole life-style needs a re-think, a close examination of how to make changes for the better. Less junk food, more healthy food, less stressful running around, more good exercise; these are the changes they need to make. Like the joke says, if they really want to change, then it can be done. It requires psychological and physical strength, but as the old saying goes: "Where there's a will, there's a way."
Then there are people who continually look at the negative side of everything, with a cup half empty instead of half full. For them, it is a matter of viewing the consequences of such an attitude, such as loneliness and discontent. Change for them is a matter of perception and a weighing of the benefits of thinking differently. There are thousands more examples, but no need to labor the point.
Change is about standing back, taking stock and weighing up those consequences of staying the same as we are or moving forward to a different, more positive place. We humans are incredibly strong, intelligent and inventive, no matter what our circumstances may be. So if we recognize the need for change, then gather up the knowledge and resources to make it happen, then as human beings, we really can change the way we are.