What it does to a planet
Leo warms a body and makes it durable. Mercury in Leo speaks with conviction and dislikes being corrected; Venus in Leo is generous and expects the gesture returned; Saturn in Leo produces someone who worked very hard for recognition that arrived late, if at all.
The generosity is not performance, though it is often performed. Leo placements genuinely give, and they genuinely mind when it goes unacknowledged, and both facts are the same trait.
Why the need for an audience is structural
The Sun rules Leo, and the Sun in a chart is what a person is driving at over a lifetime. Anything in Leo becomes attached to that project, and a project needs a witness to confirm it exists. The need for recognition is not vanity in the moral sense; it is how the sign checks that it is on course.
The failure mode is obvious enough: when recognition is withheld, a Leo placement can escalate the display rather than examine the work. Aquarius opposite is where the correction sits, in doing the thing regardless of who notices.
Fixed, which is the underrated half
Leo shares its modality with Taurus, Scorpio and Aquarius, and the family resemblance is real: all four are hard to shift. A Leo placement will hold a position for years, which is why the sign produces so many people who are still doing the thing they announced in their twenties. That persistence is the part most descriptions skip in favour of the drama.
The misreading
Leo is described as arrogant, which confuses confidence with the display of it. Many Leo placements belong to people with quite ordinary self-assessment who simply perform certainty because the alternative feels like letting everyone down.
Leo as a sun sign, and the confusion that causes
More people encounter Leo as a sun sign than in any other position, and horoscope columns have built a caricature on top of that. Since the Sun rules Leo, a Leo Sun is genuinely reinforced: the sign's qualities and the Sun's function point the same way, which is not true of most sign and body combinations.
That is why a Leo Moon or a Leo Mercury behaves so differently from the caricature. The Moon in Leo needs its feelings acknowledged and is otherwise perfectly unassuming; Mercury in Leo speaks with conviction and has no particular interest in being looked at. The theatrical version belongs to the Sun, and even then chiefly when it is close to an angle.
Questions people ask about this
Do Leo placements need constant attention?
They need recognition for the work, which is not the same as constant attention. A Leo placement doing something unwitnessed for years is common and quite stable.
Why is Leo ruled by the Sun?
It is the only sign the Sun rules, and it takes the Sun's function directly: a single unified purpose the rest of the chart organises around.
Is Leo like Aries?
Both are fire, but Aries is cardinal and starts things, while Leo is fixed and sustains them. They behave very differently over time.