You are wrong twice there... sane people make that bet every day by smoking (limited upside gain, risk of ruin loss) and by taking many prescription medicines that have side effects including death.

Using a cell phone is taking that bet. You are betting that 50 years of cell phone exposure won't cause brain cancer. Nobody knows for sure yet, nobody has had cell phones for 50 years. I'm not saying it will or it won't cause cancer. I don't know. But it has the possibility of risk of ruin.

Second, constant amount betting does have risk of ruin even with an edge. Take a fair coin flip where you start with $500 and get $51 for heads and lose $50 for tails. A clear edge with a constant betting amount. In 100 flips, you have a 27.23% chance of ruin.

For more information consult the concept of "Gambler's ruin" https://en.wikipedia.org/wiki/Gambler%27s_ruin