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Odds and Ends
We’re gonna need a bigger boat
6 7, 8:32pm
As many others have already explained, "fishing enough for the day" is pretty vague and can mean that you are taking that leeway into account (and it does in the original story).
Also the businessman is not telling him to fish more so that he can have a reserve in case something goes wrong, he's telling him to work more because he believes this is what makes you happy: working a lot to start a company that will make you own lots of things. Because he believes you have to suffer before being happy, you can't be happy (retire) without suffering (working your ass off). This is a very christian (protestant) way of seeing the world and that is what this story makes fun of.