If you get into the commander format from one of the other formats in Magic, it can be tricky to change the way that you evaluate cards for deckbuilding.
Instead of thinking about addition when you build your deck, think multiplication.
Card Advantage is a fundamental theory of Magic. If you've played competitive Magic for a while, you know all about card advantage. Here's the short version.
Imagine that at the beginning of a game, you get to draw your entire deck and you don't lose for not being able to not draw a card. Your opponent draws a regular hand. And go!
What happens?
Well, your deck becomes super-consistent, for one. You never miss a land drop. You always have the card you need, right when you need it. And, you can put together sick combos without too much trouble. Having access to all of the cards in your deck makes it nearly impossible for you to lose.
Silly right? Now, flip the situation around.
Imagine that at the beginning of a game, you draw a regular hand. But! Your opponent doesn't get to draw any cards, ever.
Now, what happens?
You are likely going to win this game, too. Your opponent will never make a land drop, never have an answer to your threats, and can never assemble a game-winning combo.
In other words, having access to more cards than your opponent means that you have more answers and more options, more consistency, and therefore a higher chance of winning.
So, in a normal game of Magic, how do you get card advantage?
There are lots of ways to think about card advantage, including "virtual" card advantage, but for simplicity's sake, consider this. When you cast a spell like Sign in Blood, you use one card (the spell) to get two cards back. You are +1 card. But you actually have 2 new cards since the spell you cast replaced itself.
It's like a minor version of what I described above. You are now ever-so-slightly closer to the situation where you have all the cards in your deck and therefore all of the options. Maybe it allows you to make a land drop you otherwise would have missed. Maybe it gives you the removal spell you needed, right when you needed it. Maybe it even gives you the game-winning combo piece.
This is called incremental card advantage and it's usually the only kind of card advantage you can get consistently. Many competitive decks are built around this concept (or around virtual card advantage).
The reason this works is easy to see. More cards = more options = more winning. In competitive, one-vs-one Magic, your opponent is not only trying to get the same incremental card advantage you are, they are trying to stop you from doing the same. So, it's a battle of little victories. A few cards here. A few cards there. These incremental advantages add up until a critical mass is reached and then boom: we have a winner!
What does this have to do with commander?
Everything! You may be inclined to build a deck that "adds up" these incremental advantages. Popular cards in the format like Cultivate and Solemn Simulacrum do this. There's nothing wrong with it. It's the backbone of getting consistency out of an otherwise unwieldy pile of 100 cards. But at some point in the game, you want to stop adding and start multiplying.
Commander games are won and lost by the most overwhelming positions. In competitive, one-vs-one Magic, games are often won by the person that can force through that one extra attacker, that one extra point of damage, or that one extra counterspell. Commander isn't often like that. It's usually a cataclysmic explosion of card advantage that wins the game.
You don't get killed by one unblocked attacker, you get killed by 1000 trampling tokens. You don't lose to your opponent resolving Ancestral Recall, you lose to your opponent resolving Enter the Infinite. (Hey! That looks familiar.)
That sort of thing happens a lot. If not that, it's the "get to 14 mana and take infinite turns with Beacon of Tomorrows and Planar Portal." Or, "Kick Rite of Replication on my Blightsteel Colossus with Warstorm Surge in play." Heck, I get killed by swarms of Pegasus tokens more than is healthy thanks to Stormherd. And don't get me started on Tooth and Nail.
To put it another way, I can sit around all game long getting incremental advantage and still get blown out by a crashing death wave. You can't counter everything. You can't stop everyone. And by turn 10, everyone will be able to do something crazy, every turn.
Here's a fun combo:
Doubling Season + Almost ANY Planeswalker
How about Planeswalker ultimates the turn they come into play? Seems good, right?
There's nothing incremental about that. It happens and suddenly where there was nothing, there are now game-breaking emblems. Lurking Predators is another card like this. Cast it and pass your turn. By the time it's back around to your attack step, it's clobberin' time.
The best part about this is that overwhelming card advantage is fun! It's more-or-less unique to the slower, multiplayer formats like commander. And, it's an epic way to end games that, if done right, actually make losing exciting.
Incidentally, this is what makes combo so "good" in the commander format. You have all kinds of time to put the combo together. And when it goes off, you are duplicating the situation where you get to do stuff and your opponents do not that I described earlier. Basically, you win because they can't do anything about it. This happens a lot too, but it's not as much fun.
Why does it feel better to lose to a massive army of elf tokens instead of
Laboratory Maniac Doomsday combo? I don't know. It just does. At least you are getting attacked. There's some level of interaction. But, to each their own.
The point of all this is that card advantage matters in commander the way it does in other formats, but on a different level. Incremental card advantage, which is a staple of successful decks in other formats, only goes so far here. In this format, you really have to pour it on. You have the turns and mana to get there, so cards like the aforementioned Rite of Replication can swing the game so far into your favor that it's overwhelming. Insurrection often does the same. Genesis Wave is nuts.
Here's an exercise: Go through your deck and identify if a card is there to give you incremental advantage or if it gives you mind-shattering, game-breaking, crippling advantage. If the second pile is looking weak, you aren't doing yourself any favors. And, you probably aren't making the game fun for everyone else either.