No one can feel a probability that small
The problem with tracking tiny probabilities like 0.0001%, aside from the rather larger chance of human error, is that no-one can feel a probability that small. If you must talk about such numbers anyway, remember: though you can write a symbolic description of this probability, a feeling that small doesn't exist, doesn't fire enough neurons or release enough neurotransmitters, so it's not actually an object worth keeping track of consciously (you'd lend it overmuch respect), any more than any Flying Spaghetti Monster proposition.
So when the math gives you a number this small, discount the hypothesis entirely. The only cause for doubt is the question of whether you did the math correctly. The thought "ok it's tiny, but not zero, so there's still a chance, right?" is one you should be wary to ever find yourself generating.
Plus if you Visualize probability as shades of grey, the human-perceptual difference between the black of 0.0001% and the black of 0% is… indistinguishable. Why then keep any track of 0.0001%?