I say you buy $10 worth of bitcoin and promise not to sell for 2 years. I'll stick $10 extra in an index fund and not sell that for 2 years. There, now we've

I say you buy $10 worth of bitcoin and promise not to sell for 2 years. I'll stick $10 extra in an index fund and not sell that for 2 years. There, now we've made an implicit wager with each other and this way we won't have to reconnect in 2 years to work out exactly who won how much.