Fine answer
Nothing to argue with here. You have to be comfortable with risk of ruin. My 400 units was always based, more or less, on the fact that, if I lost the entire bank (I never did), I could always replace it fairly easily and quickly. So, in reality, maybe 400 units wasn't, truly, my "bankroll."
In any event, for any player, it behooves him to simply plug in the numbers and generate a risk of ruin. For some very good games, especially when back-counted, 400 units is MORE than adequate, in my opinion. For mediocre, and/or "play-all" games, you need considerably more bank.
Don