In a game of Magic you have to manage several different resources. There are the obvious tangible resources like your life total, creatures, or lands, and there are the less obvious intangible resources like information. While most people have a fairly decent understanding of how to use their creatures and lands, in my experience it seems most people are less familiar with how to use information. It's impossible to say something like which resource is most important, but what I do know is if you want to win consistently you need a decent command of more then just your creatures and life.
Over the course of my career, I've found that when I have been playing my best Magic I have frequently done better at the Pro Tour than I have in our local drafts. That might sound absurd but it's because of the kind of game I play. Let's start with your average Constructed match. If it's an established format and you and your opponent are playing fairly popular decks, then you have probably already played the matchup several times and you have a good idea of what the opposing deck is looking to do on each of its turns. What's interesting is that the same is probably true for your opponent. How does this come into play? Let's look at a common scenario.
We are playing type 2 Boros against Jund. We had a fairly slow start and just put out an Elite Vanguard and a Goblin Guide over our first 2 turns. This leaves us with 5 cards in hand if we were on the draw and didn't take a mulligan. Our opponent played Savage Lands the first 2 turns and it's now his third turn. We naturally are expecting him to cast Sprouting Thrinax. If he doesn't we would assume he doesn't have one in his hand. This seems fairly straitforward and obvious because the Thrinax would be by far the most influential card he could play. He knows we probably have Path to Exile in our deck, but even if we have the Path, getting the Thrinax Path'ed isn't that bad for him. The extra land will probably accelerate him into Bituminous Blast and Broodmate Dragon, and our ensuing attack would only take him to 12.
On the other hand, if we don't have the Path, the Thrinax will completely shut down our offense. Instead, our opponent casts Blightning. Now what do we do? We consider all the known information and make our best choice of which two cards to discard. We look over the lands, creatures, and life totals, but that's not it. We also consider what we know or think we know. In this example, we believe our opponent doesn't have a Sprouting Thrinax in hand. Using this information we are more likely to discard our Path to Exile and we will make our plays on turn 3 assuming our opponent doesn't have Sprouting Thrinax. What if our opponent had a Thrinax the whole time? Our assumption that he doesn't and making several decisions with that in mind obviously has value to him. Is it right for him to Blightning us then, or was the right play for him to cast the Sprouting Thrinax?
When you start thinking like that it's easy to be too tricky for your own good. Part of why I retired completely from the Pro Tour in 2004 was because I didn't have the time to dedicate to Magic that it takes to be well-practiced and familiar with situations like that one. The right answer to that scenario depends on which cards you have in hand and what you think you can get your opponent to discard. How much does playing the Blightning actually accomplish for you? If you have a Bituminous Blast and Broodmate Dragon in hand, you may actually want your opponent to Path your Thrinax. That might help you win the game even more then him discarding the Path. On the other hand, if you have no other creatures but are holding a couple removal spells, you may really need that Thrinax in play and casting the Blightning first may be exactly what you need to do to win the game. Of course, what if your opponent doesn't bite and keeps his Path to Exile. Now you may be really in trouble, since he will still have the Path and you will almost certainly lose once you spend a turn casting Thrinax. The fear of this happening causes a lot of good players to always cast the Thrinax in this situation.
This fear is what prevents a lot of good players from being great players.
This type of situation comes up all the time and in ways you probably never imagine. That particular example is just one way the exchange of information between players can add value to your efforts to win the game. Another is bluffing. Just about everyone should be familiar with what a bluff is. However, I think a lot of people bluff simply because it seems safe to do so, without really considering all the possibilities. There are far more important ways to use bluffs to your advantage. In fact, if your deck has a completely overpowering late game, even if you are pretty sure your opponent isn't going to block it might be completely wrong for you to make a bluff that accomplishes dealing two damage to your opponent. I think most people are aware of all of that and play with that in mind, but it goes deeper.
Lets say when you attack with your 2/2, your opponent doesn't block with his 3/4 because he also has out a 2/2 flyer and he saw your Volcanic Fallout in a previous game. Your bluff just dealt him two damage, but more importantly it also communicated to him that you are probably holding Volcanic Fallout. Information is once again exchanged. Until you pass on an obvious time to play your Fallout, your opponent may make choices based on you having Fallout. These choices can easily help you to win a game.
On the next turn, for example, he will probably choose to play a Canyon Minotaur over a 2 or 1 toughness evasion creature because he doesn't want to get blown out by your Fallout. If you are holding a 5/5 that you are going to drop on the following turn, then this could be huge. On the other hand, if you are holding a creature that has the ability to tap to give a creature -2/-2, him playing the 3/3 instead of the 2/2 could end up costing you the game. If you didn't attack with the 2/2 into the 3/4, instead of him suspecting you did have Fallout, he would probably specifically think that you didn't.
Let us say it's a similar situation but your opponent hasn't seen the Fallout yet. If his 3/4 is a fairly good creature, say a Rhox War Monk, and his 2/2 out is a nice evasion creature, he will be fairly certain we don't have the Fallout-type card when we don't attack. This might lead him to play a game-winning spell on the following turn that makes four 2/2's instead of casting a second evasion creature to get us to use the Fallout. It is of utmost importance that your bluffs help you to accomplish your goals and don't work against you even when they succeed.
It is always important to be aware of what your main goals are in a game of Magic, what choices you can make to accomplish these goals, and what choices might seem like they help you but could be working against you. There are countless other ways and times you exchange information with your opponent. I can't lay them all out but hopefully by reading this you can be more mindful of what your decisions are really saying and what they are really accomplishing. My friend Crosby used to define greed as giving up more substantial long-term gains for short-term immediate profits. This kind of greed can be extremely enticing and detrimental to your Magic success. While it is easy to see the impact the Thrinax has on the board now, the long term gains from casting the Blightning in that situation are much tougher to see. Magic really is all about the big picture, not the small gains, and through proper use of information you can take over almost any game. You WILL cost yourself games in the process. It is obviously a more difficult and more complicated game when you start calculating what you can give up now to accomplish more later on, especially when it is in situations like the Thrinax example where you are relying on your opponent to pick up what you're telling him and use the information. Don't be greedy and don't be scared, play great Magic.