Earning power is something used to not only describe a business's ability to generate income or profit but also that of a person.
You can have all sorts of different earning powers/abilities/skills, like skills, knowledge or even a certain type of attitude (being pro-active for example).
What are your earning powers? And do you work on them continually?
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I'll give my own inpute aswell:
My earning power has Always come from being very, very pro-active and seeing the commercial side of things.
Where other people, even those with great knowledge and skills, seem to just want to do their job and nothing more, I am Always looking to bring people together and find a way to create a product or service that are marketable.