Jack Canfield popularized this in one of his books I heard him mention it in speeches.
Basically, the activity from which you'll find the most success in life, is something that isn't a grind for you. It's natural and easy, and you're good at it before you have even been taught how to do it. I did a Periscope live stream on this exact topic a week and a half ago; if you missed it the recording will be on YouTube in a month or two.
[There's something a few people have told me I'd be great at -- I have never done this particular thing on a for-hire level. Yet. I will.]
Disclaimers:
This doesn't mean that you will never need to do hard work to get high levels of success at your chosen activity.
I don't know if this means you're doing the wrong thing -- but you know.
Canfield has written many books -- he came to prominence via his Chicken Soup series. Look him up if you want to know more. Many of his speeches are on YouTube.