Pre-Sideboarding for your Metagame?

[Parcher]

I need an opinion on my current situation.

I am playing a deck that has certain very good matchups, and certain very bad ones. There are little to no mediocre ones. This is all pre-sideboard.

I have room to play a card in the main that does a lot to shore up the bad matchups, but is fairly usesless in the good ones. While there is nothing relevant that needs be removed to add it, it would still be a dead card in these.

The problem I have is that my local meta is heavily populated by the decks I have a good matchup against(hence my deck selection)

I can run the card in the sideboard, but I actually have less flexibility there, and end up around 40-45% against certain decks in game one.

Figuring about 25-30% of the field will be the more difficult matchups, is it worth running this card maindecked to shore those up? It's probably a 20% increase in win percentages compared to a 5% decrease in wins against my better matchups. But the better matchups will be 55-60% of the field.

EDIT: I neglected to mention that it is a combo deck. While it has tutors, it's deck manipulation is minimal. I would need to run 2-3 of the card to see it in an effective timeframe.

[Sextiger]

It's usually not a bad idea to maindeck some form of hate if you expect to face some decks, especially at the top tables.  If your running Brainstorms, then there is probably no reason not to run that card because you can simply get rid of it when it is not useful.  A lot of Control  decks now run one REB which is surely useless in some matches but it will just get shuffled away when necessary.

[OfficeShredder]

From the "low" winning percentage you gave for the bad matchup, you make it sound like adding this card maindeck will make all your matchups 60+% game one.  Why wouldn't you go for it?

[Parcher]

No, no. It makes the bad matchups closer to 60% game one, but reduces the good ones to 50/50. It also allows my opponents to sideboard for it in both games two and three, which is easy to do for most decks. Also, it hurts the consistancy of the combo as it is a "Hate" card, and does nothing to advance the deck's gameplan, only to hinder my opponent's.

This question was also intended to be somewhat theoretical. As in "Do you pre-sideboard hate for a known meta, even though it may hurt the consistancy of your deck?"

Like people running maindecked Misdirection in Vintage Fish when they expect Control, or Maindecked Swords to Plowshares in Legacy Goblins when the expect big Aggro. Cards that normally should be sideboard, but you know you will face a great deal of the decks they are good against.

[The Atog Lord]

Parcher, excellent question.

The fact of the matter is that the decision rests on a simple calculation. The calculation requires that you understand both your metagame and how well you do against the various decks in the metagame. Your goal is to maximize the number of games you win. Let's examine the numbers.

Let D be a deck in your metagame.
D.portion is the portion of your metagame which is deck D
D.without is the probability that you beat deck D without adding the card
D.with is the probability that you beat deck D with the extra card added

For example:
Suppose that Fish is 20% of your metagame:     Fish.portion=0.2
You beat Fish 30% of the time without the card in your deck:     Fish.without=0.3
You beat Fish 50% of the time with the card added to your deck:     Fish.with=0.5

With this data, calculate two numbers:

Expected_Without =
For every deck D,
add together (D.portion * D.without)

Expected_With =
For every deck D,
add together (D.portion * D.with)

Now you have two numbers: Expected_Without and Expected_With
If Expected_Without is greater, don't play the card.
If Expected_With is greater, do play the card.