Proverb about falling seven times: why stand up *eight*?

I have a question about the implications of the proverb “Nanakorobi yaoki” (七転び八起き), often translated as “Fall down seven times, stand up eight.” I’ve come across similar non-Japanese sayings, which instead match the number of falls with the number of times one is to rise—the Japanese saying seems to assume instead that one starts out on the ground, needing to get up. Is this so? And, if so, does this indicate anything about Japanese attitudes toward achievement, endeavor, or adversity?

I should add that some trace the proverb to [the Hagakure](https://www.libertyreferences.com/hagakure-the-book-of-the-samurai-01.html):

>Bad relations between retired and present rulers, father and son, and elder and younger brothers develop from selfish motives. The proof of this is that there are no such bad relations between master and retainer.
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>It is unthinkable to be disturbed at something like being ordered to become a ronin. People at the time of Lord Katsushige used to say, ”If one has not been a ronin at least seven times, he will not be a true retainer. Seven times down, eight times up.”
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>Men like Narutomi Hyogo have been ronin seven times. One should understand that it is something like being a self-righting doll. The master is also apt to give such orders as a test.