Bases for Bankroll Recommendations?

[stuey_thekid]

What figures are the 300BB limit and 20 buy-in no-limit recommendations based on? Considering you can miss draws many times in a row even while being given correct odds (hell, even drop the gloves big, open-ended straight flush draws). And sometimes repeated draw outs take place against your big pairs, two-pairs and sets even after being denied proper odds. Is there some sort of assumption that variance will only step the numbers X amount outside of expectation within a certain number of trials?