Gurley's test for true passion is whether you would study the topic in free time instead of consuming entertainment.
“I have a test that I think is the right test for whether something is the type of passion where the tools in this book could help you be successful.”
Gurley quotes Angela Duckworth saying perseverance cannot hold without sufficient passion underlying it.
“she said what she's learned since she wrote it is the perseverance part can't hold if the passion part's not strong enough.”