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I guess what I'm trying to say is if it's a +EV bet but allowed only to take once then what's the point of EV? One bet means nothing EVwise unless proven over a large sample.
That's nonsense and I don't think you believe it.
Let's see:
You can roll a dye once for $1 but if you win you get $1 million. You would take that bet, wouldn't you? And you would take it because of its massive, positive Expected Value. You can refuse to use the term "EV" for non-recurring bets and replace it with any other term if you wish (what would it be?), but it is what it is.
Nope, you're teaching EV under the wrong premise. The question you should be asking everybody is should they be taking the spot everytime it arises despite knowing that they're going to lose 83% of the time. It's not supposed to be a one off as EV can only be realized over a large sample.