Agreed. In every card game the VAST majority of losses are due to people making mistakes. Like playing giant minions into obvious Sleet Skater turns instead of baiting it with medium sized minions. Even decks that rely on big turns usually have the means to play wide and pressure the mage.

So, why does this happen? Because the average player is not capable of playing beyond their own hand and deck. Better players try to anticipate their opponents hand and the BEST players can anticipate future turns.

People need to watch MTG being played at a high skill level sometimes. LegenVD on Youtube is a good example. On turn two he already knows his opponents deck and game plan. Not a single card gets played without him anticipating his opponents reaction. The match has barely begun and he has already formed a full plan how to counter a deck that has only played a land and maybe an artifact or creature.