The first person making a mistake will usually get flamed and attacked by their own teammates through chat.
5 Things League of Legends Taught Me About Human Behavior
Alexander Germain

Making a mistake once is acceptable even for pros. Making the same mistake twice is just plain idiocy and has nothing to do with skill.

For example, you decide to facecheck a bush and the moment you reach the bush you die because one or two enemies were lurking ther. Next time you decide to do the same without having an idea were your enemies are then this is just stupid.

Not having skill is one thing and is perfectly understandable. Been stupid is not good (for the team) and this is what makes people tilted.