One problem with Borderlands 3 and other probabilistic loot games is that even when you know the drop rate you get lucky and unlucky. Sometimes it is nice to know if your boss farming experience makes sense given the drop rate of the item you are looking for.
This is where a 95% confidence interval can help you. For X trials at probability p (0.10 or 10%) in this case you see how many trials you need before 95% of players would get 1 item:
Calculating these intervals is a bit annoying so I have made a blog post to help out with the most common loot drop rates shared.
The way I use these plots is I count my farming runs say 31, then I find a plot that matches the droprate (say 10% for hellwalker) and then see the expected min and max of the interval of 95% of 31 kills: 0 to 7. So my paltry 0 items is actually quite expected at this point. sigh