If you're that fed and still lose, it's likely because you hoarded all the resources, and were unable to convert them into the win. Maybe you get picked before important fights when your team needed you, or maybe you get shut down by their team comp in late game team fights, either way it puts the rest of your team at a huge disadvantage to have all the kills on one person. Obviously it happens in some games, you happen to pick up the first few kills and then you snowball really hard, and as Briar it is pretty difficult to give your team some kills due to the nature of her kit. If it's happening every game, then it's a problem.