It depends on the gambler. There are gamblers that if they do an all in once, it's most likely that they are already fearless and likely to do that again. The risk that's taken once can easily be taken again for the second time around but it won't change the fact that the results are always varying whether you've done it before or not. And I agree that we should always gamble with an amount that we won't regret to lose.
I agree with you, and even in gambling and some other activities in life there is no specific level of risk one should take though the level of risk taking also vary from individual and at different point too but even though we don't have a specific level of risk we should take but there are still points one shouldn't exceed especially if they can not afford it. The crazy part of it is that without risk there won't be success but it has to be taken with caution, understanding and wisdom, whenever a risk is taking with the above mention there is every probability that the risk taking is moderate ( one actually used what they can afford to let go or loss).
A gambler shouldn't exceed his expectations when he's not aware of the risk that he's taking. But this is gambling and it's for sure that the risk taht we're all taking is we're all aware of. The thing is different with the amount of money that we're risking and so, if the amount isn't a lot to take, that's fine but if it's more than what we're expected to gamble, just don't be too emotional when we lose.