The probability of seeing no repeats after randomly drawing K objects out of a set of N total objects is . If you’re making your way through a really big set and 60% (for example) of the time you see repeats, then you’ve seen about 60% of the things in the set. All repeatsThere’s no line in the sand where you can suddenly be sure that you’ve seen everything in the set. You’ll find new things less and less often, but it’s impossible to definitively say when you’ve seen the last new thing. So, if you’ve seen N objects and you’ve drawn appreciably more than times, then you’ve probably seen everything.