The odds of YOU winning the lottery are pretty low. However the odds of someone, anyone, winning the lottery are high enough to keep folk buying the tickets.
And then there are those that could be beneficial, neutral or harmful depending on the outside pressures and the nature of the risks.
If the outside risk of Malaria is a bigger threat than the disadvantages of possible anemia then the Sickle Cell mutation is beneficial. But in an environment where the incidence of Malaria is low, it is detrimental.