The idea of Astrology, that you can make human/animal shapes or some other object from a random collection of burning gas balls in the sky and this somehow determines human fates/personalities makes no sense to me at all. It sounds completely illogical.
Yes, it's because you are using your left brain to interpret what is a clearly right-brained discipline. Astrology and all forms of divination are a right-brained intuitive thing, and if you just practice them instead of using your left brain to explain them you will see that you can get accurate predictions.
However there is a way to explain it. The brain has something called the "Reticular Activation System" that causes you to notice more things that are in your mind. For example, have you ever had a day where you noticed only blue cars on the street? Wherever you looked, you just noticed blue cars. Or certain numbers, like 666. That's the Reticular Activation System at work. That same system makes you notice patterns in random things, like dragons in clouds.
Now, when you ask a question and you are looking for an answer, the superconscious part of you sends a signal to your subconscious and it activates your Reticular Activation System to notice or create patterns in what you are looking at that are related to your reply. For example, you see signs or coincidences like you randomly overhear strangers mentioning a random name when you asked "who did this to me?". Also, the movement that you make (like the bones that you throw on the floor) or the cards that you draw are caused by the subconscious, so the entire thing is subconsciously done. That's how basic divination works.
The zodiac signs were created by people perceiving the sky intuitively, that's why they personified different areas and noticed intuitively different qualities that they have. That's why they all came to the same signs around the world. There is Vedic and European astrology, yet they both agree at the descriptions of the zodiac signs.