4-ofs

Last week we discussed Hypergeometric Distrubtion and introduced this series. We also discovered that if you run four copies of a card in a 60-card deck you have a 40% chance of having at least one copy in your opening hand.

Here is the introduction: http://mtgolibrary.blogspot.se/2015/12/1-ofs-2-ofs-3-ofs-and-4-ofs-and.html

So when do you run 4 copies of a card in your deck?

You want as many copies of the card as possible
My first rule is that you should consider if you would like 5, 6 or 7 copies if you could. A good example of this is Lightning Bolt in a Modern Burn deck. You would probably play 40 Lightning Bolts if you could. This is the easy 4-of.

In fact this rule is a good reason to run 3-ofs, 2-ofs and 1-ofs to include extra copies of the card. We will return to that example in future chapters.

You want to have a copy of the card in your starting hand
Well, the chance of that is only 40% (see above) BUT it is the highest chance you can get. If the card is critical to your early strategy you probably want four copies of the card.

A good example of this is the RG Landfall deck in Standard. You want to start the game with a Scythe Leopard on turn 1 so you run four copies of the card.

Here is a sample deck list of RG Landfall in BFZ Standard: http://www.mtggoldfish.com/archetype/standard-r-g-landfall-22839#online

If having more than one copy of the card in your starting hand is a problem, DO NOT run four copies of the card
If a card is critical to your strategy but would be problematic in multiples in your opening hand, you should not run four copies of the card.

A good example of this is Spire Golem in Pauper Delver. This card is an excellent card for the deck but having two Spire Golems in your starting hand will make you very slow. Thus, do not run four of this card. This is a basic probability mistake made by players who do not care enough to do the math.