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Supposedly, this shouldn't matter, since every bet involves two parties and so the sum total is zero. This ignores counterparty risk, i.e. the chance that the other person will fail to deliver when the time comes. It's the sort of thing that busted the UK's oldest bank, Barings.
From what little I understand, the derivatives market suffers from much the same complexity and obscurity as the packaged mortgage mess - the dealers are making loads of bets with loads of other people - so the misery could get spread around rather than just take down one or two incautious players.
If just 1% of the derivatives market fails, this equates to some 18% of global GDP. We in the UK are dealing with an economic contraction of less than 6% year-on-year, and that's causing paroxysms.
An argument for holding some emergency cash, away from the banks?