Even if it was ninety percent their fault, your ten percent is the only part you can fix.

Working out the percentages is satisfying and it gets you nowhere. Even when the split is wildly in your favour, the only piece you have access to is yours, and it is the only piece that can behave differently next time. The other ninety percent belongs to somebody who is not asking for your advice.

Name your ten percent out loud and do something about it this week. Not as a concession about who was wrong. It is simply the portion that comes with a handle attached, and gripping it is how these situations stop repeating.