1. You love it but you aren't great at it.
So she took a guy who was really enjoying his writing but wasn't as good as other writers. She steers him into a different job as a career so now he can work 9-5 at a job he doesn't like so he can retire and get back to his first love writing (Ok so I'm projecting he would still be writing if it was his choice).
If he really loved writing, then he no doubt continues to write to this day.
One of the ways that doing what you love can trip you up is when your passion is not internal but external. Perhaps the guy Scott didn't really love writing, he loved the idea of 'being a writer'. That is an externally imposed passion. If you love something so much that you do it whether or not people are paying you to do it, then you are passionate about the action. If doing what you do for work has no appeal to you outside of your workplace then its probably not 'love.'
2) Your skilled at your passion but hate the work that surrounds it.
Here she uses a graphic designer who loves to design but quits her job to run a graphic design business. Then she finds she hates running the business. Doh! Those are two different jobs, running the business vs doing the graphic design. Now if the graphic designer knew someone who loved to run a business but didn't care much for the actual graphic design work, poof, match made in heaven.
I've watched engineers who loved to code crash and burn when they wanted "to do more leadership" kinds of things. Its a different job, it has a different reward/influence structure, and its not at all like being able to code faster. For them, going back to coding returned them to balance and a much better level of happiness overall.
3. Your too emotionally attached
Her example here is completely flawed, her 'failure' is a woman who wanted to help kids from N. Korea get adopted but instead is credited with cleaning up a polluted river. Ok, for one it wasn't clear if what Marion Stoddart loved helping people or loved helping kids in need of adoption. It certainly sounded like it was more of the former, just her first notion at a way she could help was adoption.
Her second example is that writers who get too close to their work never improve. But that is a false dichotomy, improve by what standard? And what is too close? Sure you can have personality traits that make it more difficult to make money at what you love but it doesn't change the fundamentals.
4. No one will pay for it.
She completely shows her true colors with this one. If doing what you love is 'about the money' then you are doing it wrong. It is absolutely true that in order to survive you will need either an income stream or an ability to successfully barter for your basic food, clothing, and shelter needs. That being said, I have yet to hear of a single thing that people 'love' to do for which there isn't some way to earn enough to keep you fed and housed and clothed. (One of the high school students I was mentoring piped up at this point in my conversation 'I love to smoke pot.' I had to take a moment to point out that, while it was clear they really enjoyed it, that instant gratification was more akin to lust than love in this particular case :-)
I think the author is saying "If you are normal like me you love money like I do and so if what you are doing can't get you as much money as you could get doing something else you are stupid." And sadly a lot of people hold that particular statement to be true.
Those same people can sometimes get very depressed around middle age, the halfway point in life expectancy, where they see 'the other half' of their life which is left and so far they have yet to have enjoy significantly the 'first half' and there is no 'third half.' Contrast that to people who have spent the first half of their life underpaid but loving what they were doing for most (if not all) of their days. If you imagine yourself, lying in a bed, slowly dying for whatever reason, what is more comfort to you? Your memories of doing the things you love or knowing you've got a huge bank balance?
Growing up in Las Vegas I developed an unusual relationship with money. All around me people some days had "lots" of money and some days had "none." One of the girls in my high school's father was a professional poker player. He bought her a Cadillac when she turned 16, but couldn't afford the cost of running the air conditioning one summer. So I have always viewed money kind of like gasoline, in the sense that if you have enough you can drive a car from point A to point B, but if you have less perhaps you need to drive a motorcycle instead, and if you have none at all then its going to take a bicycle or walking to get there. It changed the flavor and the planning of the journey but it has never changed the destination.
Summary:
1) It's not about money, its about loving what you do.
2) It's about the doing not the idea of someone who does.
3) When you're dying, whether by age or by a drunk driver's hand, you will be better off if you can look back on your life with fondness rather than feeling cheated that you had not yet gotten around to doing what you really wanted to do.