There is research showing that people of lower status or authority speak up less during discussion and have less credibility. So these people have little influence on group decisions. They internalize this too. They belief less in their own ideas and are more likely to let themselves be convinced by weak evidence.
So you need to do two things to be successful. You need to convince yourself that you are a leader. This will allow you to be more confident, speak up more, and be more willing to stick to your convictions.
Then you need to convince others you are a leader. This will cause them to listen more to you, and be more convinced by what you say. This research also shows that they will like and respect you more.
And none of this depends on the quality of your opinions or evidence. All it takes is a little confidence, both internally and externally.
Why is this fodder for a blog on Human Factors? Think about it and let me know what you come up with. Hint - there are some pretty common decision making biases that are based on confidence and perceived confidence.