Variables, chances.
If your jungle decided to play a low tier champion against a high top tier meta champion then your more likely to lose a game. If you play jhin and there is a morgana whos a morg one trick, and you dont have somebody that counters her you will lose lane, forcing you to either dodge really well which can be random, or rush merc threads and have trouble csing or lack stat power. if your doing well in solo lanes jungle can just come and mess you up. bounty system punishes good players for no reason. If your in a premade and have yi you can't stop him by yourself, and you can't count on your team to do the right thing. If your laning against teemo as a melee your gonna get bullied off cs and it will continue to happen no matter who you are, what runes you have, you can have 16 magic resist from runes and rush a null mantle into hex, you will still get bullied.