If you prepare well and still find the decision already made by the time you speak, you are not being ignored and you did not prepare badly. You arrived one conversation too late. Most decisions are settled in short exchanges before the meeting, and the meeting confirms what those exchanges already agreed.
That is not a conspiracy. It is how most organisations above a certain size actually work.
Where the decision really happens
A quick word in a corridor. A message asking what someone thinks before an agenda goes out. Two people who spoke on Tuesday arriving Thursday already agreeing.
By the time everyone is in the room, the shape of the answer usually exists. What happens in the meeting is people checking that shape holds.
This is why the advice to prepare harder does not fix it. You can walk in with the best argument in the room and still be too late, because the argument you needed to make was on Tuesday, to one person, in three sentences.
Why this hits some people harder
If you think before you speak, you are at a disadvantage twice over.
You want time to form a proper view, so you often are not ready to say much on Tuesday. And the corridor conversation is exactly the kind of quick, unplanned talking that costs you most energy, so you avoid it without deciding to.
Erving Goffman described the difference between what people do on stage and what they do off it. Meetings are the stage. The real work of persuading happens off it, and it is shorter, rougher and less formal than the meeting you prepared for.
Nobody explains this. Some people work it out early, usually because they are comfortable with unplanned talking. Others keep preparing harder for a stage where the decision is already made.
What to do instead
Not more preparation. Earlier and smaller contact.
Before a decision meeting, find the one or two people whose view will carry it, and say something to them beforehand. Not a pitch. One sentence about what you are seeing, and a question about what they think.
That does three things. It puts your view in the room before the room fills. It tells you what has already been agreed, so you are not walking in blind. And it lets you say your piece to one person instead of eight, which is a much smaller thing to do.
You can send it in writing. It does not have to be a corridor conversation, and it does not have to be long. Two sentences before a meeting will do more than twenty minutes of preparing for it.
How to work out who to talk to
The obvious answer is the most senior person, and it is often wrong. What you want is whoever the decision actually waits on.
Think back over the last few decisions on your team. Whose objection changed something? Whose agreement made everyone else relax? That person is worth a message beforehand, whatever their title says.
There is a second name worth having. Who tends to know things first? Not the decision maker, but the person who always seems to have heard already. A short question to them tells you what has been agreed before you spend any effort arguing about something that is closed.
One caution about your own manager. If you are going to speak to their peers or their boss before a decision, tell your manager first, even in one line. The same message reads as helpful if they knew it was coming and as going around them if they did not. That is not about politics, it is about not surprising the person whose support you need most.
Start with one name and one message before the next decision meeting. You do not need a strategy for this, you need to be one conversation earlier than you were last time.
What stays yours is the specific read on your own team. You know who those people are in a way no article can. What this gives you is what to look for.
Most people find the name faster by describing how the last few decisions actually went than by trying to work it out in their head. Said out loud, the pattern is usually obvious.