Where it expands
Horizon. Travel, study, foreign languages and the general project of finding out what is over there all pay off here, and the placement keeps arranging its life so that more of them are possible.
Meaning expands too. This Jupiter needs what it does to signify something beyond itself, and it will take a materially worse arrangement in exchange for one that does.
What it overdoes
Certainty. A conviction reached here is held at full strength immediately and defended in public, and the absence of any moderating influence in the sign means nothing slows that process down.
It also overdoes physical appetite and promises. This Jupiter agrees to things sincerely, at scale, in the moment, and the honouring of them is a separate question it has not yet reached.
What it is actually generous about
Opportunity for other people. This Jupiter opens doors, makes introductions and vouches for people on limited evidence, which works out often enough to justify the habit.
It is also genuinely generous with belief in someone — telling them what they could be rather than what they are. What it does not supply is the follow-up, and the recipient is left to do the work alone.
Why the dignity is what it is
Jupiter rules Sagittarius, so the planet is operating in a sign built to its own specification. Mutable fire spreads and enthuses, which is what Jupiter does anyway, so nothing here is being filtered.
Rulership does not mean the placement is good. It means there is no friction between what the planet wants and what the sign supplies, so the expansion arrives undiluted — the excesses at the same full strength as the generosity. Dignity is about fit, not about quality.
Against the opposite sign
Jupiter in Sagittarius faces Jupiter in Gemini, where the planet is in detriment. Sagittarius concludes and commits; Gemini keeps collecting and never closes, and each considers the other's method careless.
The axis is the useful unit. Sagittarius's development is the Geminian habit of holding a conclusion loosely enough to revise it, which this placement finds harder than any of the things it is celebrated for.
Questions people ask about this
Is Jupiter in Sagittarius the luckiest placement?
The tradition treats it as the planet's most characteristic position. That is a statement about fit rather than about outcomes, and the folklore about luck should be read as folklore.
What does this placement overdo?
Certainty and promises. Both are issued at full size, and nothing in the sign moderates either.
Why is Jupiter in rulership in Sagittarius?
Dignity names the fit between planet and sign. Sagittarius is Jupiter's own fire sign, so the planet's traits arrive undiluted, including the unhelpful ones.