[Fomite]

Buying a lottery ticket is rational if the cost of the ticket is offset by the relative increase in your pleasure that comes from dreaming of winning.

For example, if you gain >$price of a Powerball ticket worth's of entertainment from musing about how you'd spend the prize, it's a rational purchase.

On the other hand, buying two tickets isn't rational. You get no extra dreaming, and your expectation of winning hasn't moved essentially at all.

[sanoli]

Not really. If you buy 10 tickets, you're buying an extra dose of thrill because you think "I bought ten, I got a better chance of winning".

[Fomite]

My assertion is true even for people who understand probability, and thus won't get much thrill about multiplying ~0 by 10.