Time until the bet is over- If today is December 31st, 2022 and the price of Tesla stock is four times the price it was on January 1st, 2022 then it is very very likely that the price the following day will be at least two times the price it was at the beginning of the year, because it is unlikely the stock goes down more than 50% overnight. So, a rational derivatives price would be very very close to $10, say $9.95. On the other hand, if it's month 3 (9 months of the bet remaining) and the price is four times the price at the beginning of the year, it seems somewhat likely that the stock will be above the two times bet price by the end of the year. But, this extra 9 months introduces some uncertainty, changing the confidence of winning the bet from very very likely to somewhat likely, so a rational derivatives price would be somewhat close to $10, say $7. Note the price of the Tesla stock is the same in both cases, what has changed is the time until the bet is over, which changes the derivative price.