Arqane said:
Can someone put together a formula that would somehow show when it's a "smart" idea to invest in a lottery ticket. I don't think the average return per dollar really shows that well.
Yes, it does. You are just not accepting the results.
Take your example of a lottery where everybody puts in 2$, and everybody, on average, receives 1.80$, and one person must receive 1B$. For this to work, there must be at least 5 billion people participating in your lottery ( = 1B / 0.20 ). This means that if everybody on Earth played your lottery, only one person would say «Damn! The system works!» A system where everybody on Earth participates, and only one person profits from it, is not a system that works. If you think the contrary, then I invite you - and everybody else on this forum - to PM me such that I can tell you how you can send me 1$ just for the fun of it.
Arqane said:
The risk someone takes with an investment usually depends on a few circumstances, and often includes subjectivity. If you had $10,000 to invest, put only $9,998 into the stock market and bought a lottery ticket with the extra $2, the math would say that you're likely to lose $0.40 from my lottery example compared to investing the entire $10,000.
This is the kind of thinking that leads to gambling addiction.
If you follow that logic, here's what going to happen (We're talking about a certainty of 99.999...%): You will lose the 2$ and end up with 9998$. If your goal is to make money, then you have to reinvest that amount to compensate for your loss. How will you do it? Well, you have that great system where you could invest 9996$ in the stock market and 2$ in the lottery because it is not that much different from 9998$ and 2$. And you will lose 2$ again. And this cycle will work like so until the 2$ becomes a bigger portion of the total amount to invest. At that point, say 100$ and 2$, your logic will change to: «Now I don't have a choice, I MUST win the lottery to regain my lost. I can't quit now.» This will last until you will lose everything because the odds of losing 5000 times in a row are extremely high.
Your only hope in such a system is that the 9998$ you invest somewhere else gives you a gain of at least 2$. If you constantly gain 2$ and continue with your investing strategy, you will end up with 10000$, no matter when you stop. If you gain more than 2$, you will make money, but you would have made more if it wasn't for the lottery tickets you bought.
These are your odds. They are only based on luck. And if you're lucky, it only means that millions of other people have lost. You cannot share your "system" with millions of people and expect that most of them will gain from it. It is not a system. It is not an investment strategy.
Real Life Example
Not long ago, it just so happen that I studied such odds. A local lottery had a 70 million $ jackpot with 1 in 33 million odds for a 5 $ ticket. But I could join a group with 70 people in it. So now my odds are about 1: 500 000 for a 1 million $ jackpot. These odds are a lot better and 1 million $ is still pretty great.
But there is more. They are other smaller winnings also available with the same ticket. The smallest one - still making me a winner once split 70 ways - was 13 $ for a 1:531 odd. That is 8 $ in my pocket! And look how ridiculous those odds are compared to 33 million! I can't pass up this opportunity!
It sounded way too good, so I tried to visualize what 1:531 meant. So there is this guy in front of me who I give 5 $ and then asks me: «I'm thinking of a number between 1 and 531. If you guess it right, I'm giving you 13 $. You only have one chance.» So what? I say «287» or «53», the guy says «Nope, that wasn't it» and I just lost 5 $. I would feel so stupid playing this game. And playing that lottery would have been exactly that.
I did not buy any tickets.