So I've seen it thrown around a lot especially in relation to the core starter box that you cant make competitive decks without 3 copies of all the cards. Can I ask what the logic or reasoning behind this is? why this is such an adamant and militant poi9nt for so many people?

 Take one copy of the core set and a few expansions and chapter packs, make some decks, go to a tournament, and then you will know. 

Zso Sahaal said:

Mostly, because the deckbuilding rules say you can have up to 3 copies of a card in the deck. People seem to think that this means you should have 3 copies of every card available to you. They seem to forget that no matter how many copies of some cards they have, they never use them. In any deck. You don't need 3x of everything to be competitive. Although, short of the Core Set (and the out-of-print Clash of Arms CPs), you get 3x of everything when you buy it, anyway.

Zso Sahaal said:

God knows. For some people, I think it is myopia and an inability to think creatively. For others, it is about deck efficiency and draw probabilities. If, for example, you are going to build your entire deck around the Asshai trait and Melisandre giving all Asshai characters +1 STR while she is standing, you are probably going to want as many copies of her as possible in your deck to improve the chances that you will draw her. But, if you build your entire deck around the Asshai trait and don't really think they need the STR boost from Mel, she goes from "key" to "gravy," and you probably wouldn't even want 3 copies of her in your deck.

1) Deck efficiency

2) Draw probabilities

3) More cards = more potential creativity -- two people with equal skill in play and deck building become unevenly matched when one has a larger card pool, ceteris paribus

4) Uncertain future; cards from current or older sets can suddenly become an instant-include if some new card is printed with which they have significant synergy

5) 3x of all cards gives you the ability to create more decks at once; you don't have to keep moving that Valar from deck to deck, etc. ;)

Honestly, it depends. A lot of the cards in the starter set are very good and the ability to run 3 of them would help a deck out significantly. But on the flip side, that's not always going to be true. A Lannister player, for example, gets more out of a third core set than say, a Martell player. Over all though I would say having a second core set is significantly more important than having a third. (Going from 1:60 chance of pulling good card X to 1:30 is much better than going from 1:30 to 1:20.) 

Golden Tooth Mines, Bodyguard, Enemy Informer, Power of Blood, Power of Arms, Forever Burning, Gold producing locations, reducers (less so now with deluxe expansions), etc…

In short, there are many cards in the core set where three are required for competitive play.

bergs206 said:

 

Maybe I should correct myself, not required but it helps immensely…

I also should mention that if you have a unique card/cards you want to build around it is nice to duplicate them.  I for one am a very conservative player with my uniques and try not to place them out until I can place a card and its duplicate out there in case someone goes Vallar on me.