What does this sentence mean?
He is working fifty percent more on his job and fifty percent less in his job. He is 100% happier.
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A popular phrasing among entrepreneurs distinguishes between working "on your business" and "in your business." For example, if you own a restaurant, working on your business includes marketing, hiring and firing, choosing suppliers, changing your sign, getting new furniture, joining an association, etc. Working in your business would mean cooking. Maybe setting the menu. It's a way to remind people they are the owner, not just an employee.
In that context, working on your job might mean politics and "managing up" or it might mean taking courses to fill in your knowledge gap, meeting your counterparts elsewhere in the business, reading about your industry and trends, going to user group meetings or industry events, golfing, going out to buy clothes that suit your role and so on. Working in your job would be writing code or issuing mortgages or whatever you are actually paid to do.
The percentages aspect of the sentence are a red herring - there's no particular meaning to the 50, 50, and 100. The important part is the in/on.