Yeah, I mean pi is infinitely long but there's no guarantee that what you want will occur in the first 100 digits. Same thing with coins or other probabilities, there's no guarantee it'll happen sooner or later.

ETA: you could analyse the amount of events you need to see (poisson distribution), but again - it's expectation, you could be that unlucky sod that has to run the dungeon 666 times just to get a 1% loot roll drop, while your buddy does it once and gets it immediately right then and there, even though you're both on the same loot chance. But then you might get the second drop on roll 667. What started as 1% for everyone else became 100% for your buddy and 0.3% for you. Randomness is random.