In many hand histories posted on this site, where hero has a good but non-nut hand and is facing a reasonably large river bet (fold/call decision), a common claim is that you only have to be 'right' 1 in 6 times (or sometimes it's stated as 1 in 7 times) to make a profit. Is anyone familiar with this, and if so, can I get further explanation? I've got to think that my understanding of this claim is way off - how can calling and losing with 2nd best hand 5 times in a row be justified if the sixth time you catch a bluff and win? I realize that dead money in the pot often makes the pot odds for calling a river bet with a potentially winning hand pretty good, but where does the actual ratio of 1/6 or 1/7 come from? This seems quite arbitrary - Is it dependent on the situation, i.e size of river bet and/or size of pot, and if so, what is the equation to figure out the profit ratio for a given hand?

I should have an example or link but I don't - I apologize if this post is complete nonsense.