Confidence in lane.
I've never seen anyone write about or talk about this but its something that can pretty heavily affect game play. Recently i played a game as swain mid. I was laning against a Veigar who at level 1 let me chase him to his tower to avoid getting E'd, for the entirety of the laning phase he got roughly 1/3 of the cs because whenever he would try to cs i would chase him back to his tower. By the time the game ended Veigar had 2/3 my cs and was 0/7, he wasn't able to recover from his laning phase so he had to farm instead of team fighting. After the game i started thinking about what happened in lane. At level one he had three options when i tried to harass him, he could fully engag and attack back, run and q-aa me back, or run as far as i'd chase him. His choice made a clear impression on how he felt against me in lane, for some reason he thought he was weaker than me. Because of this all i had to do was act aggressive and harass consistently, easy lane won. Even if i didn't get many kills denying a Veigar his farm and getting free farm yourself is an easy way to win lane. Looking back on the situation though if he had chosen either of the first options my actions towards him would have been significantly different. Had Veigar faced me and fought back it would have shown that he wasn't afraid of me, that I wouldn't have tried to push him around in lane. Even if he didn't think he could have won, pretending not to be afraid would have changed how i reacted to him.
TL;DR If you act afraid of your lane opponent they'll notice this and abuse you for it. If you act confident, even if you aren't, they'll respond accordingly.
What do you guys think about this?
a lot. You can get people to back off your partner/control where the badguys are just by acting like you're going to run at them. Sometimes it saves lives.