It's the same reason why we'd prefer to read two short books instead of one long book. Total number of pages read might be the same, but we feel more accomplished having completed two whole books.
It's the same reason why breaking tasks into bits (and then checking off each bit on our to-do list) makes us feel more accomplished and energized than leaving one, big task on the to-do list, ever unchecked.
We are completionists by nature.
Sometimes this is a bad thing. Rational decision makers must ignore sunk costs. Abandon that book that stopped being interesting at page 50!
Ben figured this out while cutting his sandwich in half for lunch proving that yes, wisdom really is everywhere.
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