When I was in a 50/50 debate/discussions, in many cases I leaned towards myself being wrong and the other being right automatically...and later would feel discontent with everyone when I turned out I was right and should have pushed harder. But I guess dont know how to be assertive without being offensive or overly brazen about my frustration.
1. Avoiding acknowledging doubts or weaknesses in the position you're arguing for.
2. Allowing a decision to be finalised when you remain unconvinced.
These two behaviours have different outcomes if you take 'outcome' to mean 'who won the debate'. But they're both flawed and they both come from underconfidence.
Confident engineers care about finding the best consensus. They openly entertain doubts in their own position (and happily change their position in front of others), and they also persist with the discussion until they're genuinely satisfied with whatever consensus is reached.
These days I temper my "I'm not certain so we should investigate this" with "but you're not certain either so you're not getting out of investigating it and admitting you're wrong if it comes to that."
You think this or that project is not solving the right problem? Speak up. You think some key result should be achievable with fewer people and sooner than what was planned? Speak up.
I learned this recently, sharing feedback that I was concerned would sound harsh, only to fall on receptive and understanding ears. If anything I should have spoken up sooner/more often!
Your team/startup/etc. will thank you.