If he's a just man, though, he must have the habit of justice, which means he habitually doesn't fall.
I don't know of a hard and fast rule for determining whether someone does something habitually, so let me propose for the sake of argument that you need to do something right at least twice as often as you do it wrong for you to be said to have the habit of doing it right.
If the just man falls seven times, then, he doesn't fall at least fourteen times.
Traditionally, the proverb has been interpreted as meaning that the just man falls seven times a day. Thus we have (rounding down) a minimum of twenty opportunities a day for the just man to fall.
Is there any reason to suppose that the just man has more opportunities than anyone else? We might suppose his reputation has put him in a position to make more choices than the average person, but in general I think we can get away with 20 as a threshold number of moral choices people make every day.
In any event, we surely all make more than 20 choices a day, and we might notionally rank them in decreasing order of how much intellect and will are brought to bear on them. The choice of answering an email might rank higher than the choice of passing a slow car, which might rank higher than the choice of putting a dirty spoon in the sink.
Of your notional Top 20 Moral Choices on a typical day, how many of them would you say are real puzzlers?
We Internet natterers spend a great deal of time nattering about identical twins and violent lunatics and amnesia and amputating arms and all the cool scenarios that test the boundaries of how moral principles are formulated and how moral action is analyzed.
But [almost] nobody spends much time at all actually living and acting in these scenarios. Ordinarily, our choices are ordinary. Ordinarily, the moral issue isn't whether I knew or ought to have known that the gun was loaded. Ordinarily, the moral issue is whether what I choose to do is something I, and everyone else, know or ought to know is right.