The reality is, some players will make mistakes. Some players have not yet learned the game well enough or understand the mechanics enough to make the right decisions. But blaming that on all tanks or all healers, or the design of tanks or healers is narrow-sighted. This is a game. That means you're going to fail once in a while, whether by your own hand or someone else's. Yet many players in FFXIV treat failure like it's a flaw in game design--that if the jobs were actually well designed, failure would be impossible, but that's insane.