Holy Trinity of League

I think this game could really benefit from some kind of game-school in the form of brief text and video guides on the holy trinity and teamwork, because it seems many don't know anything about that, yet it is so much more crucial than in PVE games.

Just now I had another match with a tank who would bail on the team during team fights each time his HP dropped below 50%, or outright ignored enemies attacking team mates right next to him because he was busy fighting minions or structures.

Fine, people don't have to do the job of the role they pick/build into, but at least put schooling info out there so people can watch/read it when they get tired of losing and having no clue why they lost.