I first got intrigued to investigate astrology, while disbelieving it as utter bunk, when someone correctly "guessed" (asserted with certainty) what my sun sign was, from my personality/behaviour. I have since gone on to be able to fathom several other people's sun signs from not only their behaviour, but their appearance[1].

But for sure, there are feedback loops.

Prediction or projection? Ever the feedback loop quandary.

[1: You can literally see it. In shorthand, by faces alone (though there are many other clues)...:

• Aries, you can see the aries glyph on their face, in the eyebrows.
• Taureans have a T on their face with a more flat eyebrow.
• Gemini have the twins facing each other on their face.
• Cancerians have a "moon face", sometimes can see a crab-like appearance too to help distinguish from Librans.
• Leos have a lion-like nose/mouth/jaw protrusion/carving.
• Virgos have the tell tale "large cheeks". [Edit: Heart shaped "spade faced" too.]
• Librans have "lightbulb head" (and a softness of features).
• Scorpios have a scorpion like severity to their face. (Like Capricorns, hard to describe)
• Sagittarian (I think the easiest to spot) have a rectangle forehead.
• Capricorn's kinda goaty, kinda see it in the severity in their eyes, and a sharpness of features (like cheekbones).
• Aquarius I find harder to spot by their face (because of uniqueness), best clue, lower top eyelids, I often mistake for Taureans.
• Pisces are best detected in the eyes that look like two fish jumping out of the water towards each other.

And if you then couple appearance with personality traits, it gets easier to see/guesstimate. Some people manage to tune their sight to see it constantly, effortlessly, whereas some people "never" see it, much like magic eye pictures. Then of course, there's rising sign and moon sign (or stelliums) that typically next have the biggest influence on appearance, which may be worth enquiring if guessing sun sign incorrectly, to see if you were seeing those other influences. Once you know what to look for, sometimes it stands out strikingly obvious.]