There are people who believe many aspect of our lives are tied to the position or movement of the sun, the moon, planets or stars. They believe that our future can be predicted to some degree by studying the celestial objects. They do not have so much as a proof to validate any of it, but believe in some facts and believe it to be true, to support it. These facts are largely unverifiable or false, but they do not care, they do not know or they do not want to know, and they continue to believe in it. But now we have an understanding of many things and if celestial objects are a major influence then we would have found some evidence for it but we haven't found any.
What we do now is because of what we did, what happens around us now and what we think will happen in the future. But there are people who believe our behavior and our character is determined by the celestial objects. As a proof they may say the moon causes tides, it exerts a lot of force over us and hence it can determine our character. But we do not find everybody happy during, say, a full moon and everybody sad, say, during a new moon. Or they may tell people are categorized into groups based on some factors. Things are common for members within a group and not for everybody. Maybe people fall into different categories according to the position or movement of celestial objects and people in the same category feel the effect of the moon or the sun in a similar way. But we do not find people within these categories exhibiting the same characters. Comparing such claims and what happens around us we can't say our behavior or character is determined by the celestial objects in any major way.
There are people who believe the moon, the sun etc affect the fluids in our bodies, our hormones etc, similar to how it affects the oceans and causes tides. So we can say there is a force acting on us due to the celestial objects and that its effects will be similar at the same place at the same time. Let us assume it affects our hormones, maybe it determines the level of hormones secreted or it determines the base level of hormones required to spring us into action. So the people who are born on the same time and same location should show similar behavior. But we know it doesn't happen that way. Maybe it is true that it affects our hormones and has a say in the basic emotions that we will have, like happiness, sadness etc. But in a majority of the cases our behavior is not directly linked to our basic emotions. Suppose our boss is angry at us and it made us angry. As a reaction to it we may be smiling, showing some guilt etc. It is so because we have an ability to feel our basic emotions and take appropriate actions based on our situation. If somebody did something very bad to somebody and he says I couldn't control myself because it was the full moon making me do it, a huge majority of the people wouldn't believe it or see it as a terrible excuse. So even if there is an effect the celestial objects have on our behavior, it is not as strong as the control we have over our behavior.
The people who believe that the celestial objects determine our future or our behavior has no evidence to support their belief. They believe it because their family or friends believe in it. And the people who study about the celestial objects are yet to find a good enough evidence linking our future or our behavior to the position or movement of celestial objects. Predicting our future or our character or behavior based on one thing, when we know there are so many things that has to be taken into account is not rational. Our family, friends or society have a far greater role to play in our character development than the sun or the moon.