There are many different actions in a game of Magic. We draw cards, cast spells, trigger abilities, and attack with creatures. We block, shuffle, sacrifice, mulligan, and concede. And yet for all of that, the only thing we ever really do is decide.
Magic is a game of decisions. No matter the format, no matter the stage, all you ever must do to play good Magic is make one correct decision after another until the game ends. Of course, as we all know, that's easier said than done. Magic is a very hard game.
I was first introduced to the idea of Magic as a decision game through, of all things, poker. There was a time in my life when I was very interested in getting into poker and started reading different books about the game. I never actually started playing poker, but I found that a lot of the theory I was reading could be applied to Magic.
The decision stuff specifically I found in a book by Annie Duke called Decide to Play Great Poker. I was enchanted by the idea that, in her words, "Poker is a game of decision-making under conditions of uncertainty." The game is all about making decisions, and the problem is that you do not have all the information necessary to figure out what the outcome of those decisions will be. This is a description of the game of poker, but it describes Magic just as well.
A few months ago, I was part of a conversation after a tournament discussing what the win rate of the theoretical perfect Magic player, someone who would always make the best possible play in every scenario, and who also had access to every piece of relevant information, would be. Said information would include not just the opponent's hand, but also the composition and order of both players' decks at all times.
Obviously, you can never be as good as this theoretical Magic player. No matter how good you are at reading your opponent, you're not going to know the order of the libraries. But if you were somehow to acquire that mystical power along with the ability to mentally process all that information and arrive at the correct conclusions, you would almost never lose.
As I put it in that conversation, this perfect Magic player would be able to make terrible plays and have them be right. They would keep no-land hands because they could see that they'd hit five lands in a row off the top of the deck. They would never be surprised by the opponent topdecking another copy of the spell they had just Thoughtseized away.
They would attack into four open mana with all creatures every time the opponent didn't have Settle the Wreckage and would hold back appropriately every time they did. And, perhaps most illustratively, they would be able to play Lantern Control without the card Lantern of Insight.
Their Codex Shredders would establish the Lantern "lock" without needing the information provided by Lantern of Insight. They'd be better than that, even, able to look past the top card and know when aggressive milling will get the opponent to a run of lands or when milling a problem card isn't a good idea because the next card is even worse. Honestly, I have a hard time believing that this perfect Magic player would ever lose a game.
The Difference Between Correct Decisions and Good Plays
Let's leave our perfect Magic player alone for a minute to bask in the glory of winning their 100th Pro Tour and consider a different scenario.
You're playing against a U/W Control opponent who has nine total lands on the battlefield, of which only an Island and a Plains are untapped. They have one card in hand, and only one life point remaining. Unfortunately, you know their top card is Approach of the Second Suns, and they've already cast that spell once this game.
You draw Shock for the turn, joining the Goblin Chainwhirler in your hand. Either will kill your opponent, but you only have three Mountains on the battlefield, so you can only cast one of them. You know that the only relevant cards in your opponent's list are two Negates and one Essence Scatter, you haven't seen either so far this game, and you're confident that the card in their hand is one or the other. What's the play?
The best play is to cast the Goblin Chainwhirler, because your opponent is more likely to have one of their two Negates than the single Essence Scatter. So you cast your Goblin Chainwhirler, and your opponent casts their Essence Scatter. You made the best play but the wrong decision, and it cost you the game.