If you're very poor and stuck in a bad situation, there could 0.0% chance you ever become a millionaire through the normal mechanisms, maybe spending $1 a week on a lottery ticket raises that to 0.00000000001% and creates a bit more hope in your mind.
Again, I'd never advise anyone to buy a lottery ticket. But if it makes you hopeful, maybe it's a better treat for yourself than a chocolate bar.