6
The washing machine
Paper tickets and laundry, a combination older than the lottery.
Tickets have been destroyed in washing machines, left on dashboards in the sun until the thermal print faded, soaked in rain and eaten by dogs. Thermal paper in particular is extremely unforgiving: heat alone will blank it.
Lotteries can sometimes verify a damaged ticket if enough of the barcode survives and the purchase can be traced, but it is entirely at their discretion and there is no obligation.
The two-second version of the fix: photograph the ticket, front and back, the moment you buy it. It is not proof of ownership, but it is the difference between a conversation and no conversation at all.
Some lotteries also void a ticket that has been altered, even accidentally. A ticket that has been laminated, taped back together or written on beyond the signature line can be rejected outright, so the instinct to protect a damaged ticket by patching it up is exactly the wrong one. Photograph it and hand it over as it is.