You say less than you know
Sun in Capricorn lands in your 3rd house, so your ordinary speech is compressed: no decoration, no speculation, nothing claimed that you cannot support. People discover the depth of what you know by accident, usually years later. You need work where accuracy is eventually rewarded rather than volume.
The trouble is that rooms are frequently allocated on confidence rather than on content. Somebody less informed and more assertive will be believed first, and you will find that unjust and say nothing about it.
Understatement is a habit with a bill
Your instinct is to describe your own contribution in the smallest accurate terms, which reads as modesty to people who already know you and as a lack of achievement to people who do not. Learn one plain unhedged sentence about what you have done and use it unchanged. It will feel like boasting and it is simply a description.
Learning is work, and you do the work
You approach a subject the way you approach anything: methodically, from the foundations, with the boring parts done properly. It is slower than other people's approach and it produces knowledge that holds under pressure. Trust it rather than envying the quick studies, because the difference shows up in the third year and never reverses.
The sibling who took it seriously
Among brothers, sisters and cousins you were probably the responsible one, and the role was assigned rather than chosen. It may still be running. Notice what you are still doing for the family communication that nobody asked you to take on, and hand one piece of it back this year to see whether anybody actually minds.
Say it before you are certain
You wait until a thing is fully worked out before mentioning it, and by then the decision has usually been made by people who spoke earlier with less. The half-formed contribution is allowed. Say the provisional version in the meeting, flagged as provisional, and let the accuracy arrive in the follow-up where you are strongest anyway.
The written record is your ground
You are more effective in writing than in live debate, and the documents you produce become the thing people rely on for years afterwards. Play to that deliberately: send the follow-up note, write the procedure, own the record. Influence in most organisations belongs to whoever wrote the version everybody now quotes, and that person is almost never the one who spoke loudest in the meeting.
Dry, and funnier than expected
Your humour is understated and lands on about a third of the people who hear it, which is why some find you severe and others find you excellent company. Nothing needs changing except the pace of disclosure. Let the joke arrive earlier with new people, since it is the fastest route through the reserve you did not intend to build.
The one told to be sensible at eleven
Somewhere early you were designated the reliable child, and the designation came with a tone of voice that is still audible in how relatives address you. It shaped a real competence and it also ended something. Notice what you are still not permitted to be in that family: unserious, wrong, in difficulty. Being one of those in front of them once, on purpose, changes the arrangement more than any conversation about it.
The unspoken thing stays in the shoulders
What you decide not to say does not disperse; it accumulates across the neck and upper back over months rather than days. The relief is delivery, and the delivery does not have to be to the person concerned. Say it out loud once, to anybody, and note how much of the tension turns out to have been in the holding.
A room cannot discount for modesty
Somebody less informed will describe their contribution in stronger terms than you describe yours, and the room believes them, because no room knows how to adjust for understatement. You have watched this happen and filed it as unjust rather than as fixable. It is fixable, and the fix is not confidence: it is one factual sentence, written down before the meeting and delivered without softening.