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The lottery is entirely rational if you can afford it as part of your disposable income. I often spend more on beer in one night than I do on the lottery in one month.
Yes the chances of winning the huge prize are vanishingly small, but there are greater chances of winning the smaller prizes.
It's also a form of giving to charity, plenty of Olympic and Paralympic athletes are funded by lottery causes.
Purely anecdata but I'm also about evens on the lottery thanks to a small (<£1000 each) lottery win as part of a work syndicate years ago.
To be clear, I'm not suggesting that playing the lottery is a rational thing to do, because it isn't.
However whilst each ticket has the same chance of winning, more tickets = more chances. Taken to extremes, the overall chance of winning would be very high, for example, if you were to buy 20 million tickets.
Edit: apparently it's around 45,000,000:1 for the jackpot so my example should be more like 50 million tickets. Same principle though.