I think your problem with this advice is that you're looking at it at the micro-scale. They don't mean the, fairly hedonistic, "only ever do the activities that you love to do", but rather in a grander scheme. Work on the problems that motivate you, the issues that are near and dear to your heart. And yes, that will mean doing things you don't like. But it also means you'll be more likely to succeed in them because you actually care about the end result.