It's the same thing with people watching, experience counts. Human beings are complex entities. The world of astrology is certainly not exempt from problems like this. Astrology is not a hard science. This is exactly the same thing as medicine.
Doctors use scientific tests, but they disagree amongst themselves.
Conflicts of opinion over the astrological meaning of a newly discovered planet arise from time to time. It took probably 30 years before the majority of astrologers agreed on what Pluto was really about, and deeper insights are always being published. Agreement by consensus, built on arguments that utilize anecdotal evidence, is how Western astrology has moved forward. Only a few truly scientific studies bolster the contentions of this field of inquiry. Mesoamerican astrology is impoverished by comparison.