Let's say I am quite sure that the Steam Machine will cost more than $700 dollars, and I buy a 'yes' lot for 65 cents on the payed-out dollar, those are the odds at my buy-in time.
Where exactly now do the other participants' bets on the same market influence my chance to win/lose? How am I up against them and not the question "will my prediction come true"?
Sure, before my buy-in the odds, and thus the value fluctuate on account of the market movements, but once I'm in I'm in?