A good analogy is is a blindfolded person throwing darts at a dartboard. The probability of hitting a bulls eye increases with the number of darts thrown at a time, and how long a person continues to throw darts.
It’s the same with radon exposure. The longer we are exposed and the greater the concentrations we are exposed to, the greater the likelihood radon will give us lung cancer.
In short, the only safe level of radon exposure is when there is no radon. In other words take the darts away from the person.
Although it is not always feasible to remove all of the radon, the wise course is to limit our exposure to it as much as possible.