It's good advice, but at the same time somewhat paradoxical. The author is essentially saying "don't force yourself to learn things; it doesn't work; instead, find something you don't have to force yourself to do and do that". The paradox is that trying to figure out what motivates you naturally is itself work--if you're in the mode of asking "I must figure out what it is that motivates me intrinsically", that's not an especially playful or fun-loving mode of thinking, so there's a good chance you won't notice.
There's also the possibility that you will find something that really motivates you, but it ends up falling pretty wide from what you originally wanted to learn--e.g. maybe you find that you really love programming, but only if it's in TI-BASIC on your graphing calculator.