How much do you earn writing a book?

I recently saw an interview with a successful german book author (don't remember his name), who was just opening a shop (I think for shoes?) in his local city. The interviewer asked him about his success, and why he is opening this shoe shop, if he hasn't earned enough with his two very successful books so far. The author looked angrily at the interviewer and said:
"Do you think I could live from my two books? Of course not."
The interviewer then was a bit confused, but I understood this man: The book I wrote costs around 14 euro, and I get 50 cent of each sale, after taxes. That means I need to sell 24000 books a year in oder to earn the Austrian minimum wage. For independent book authors, selling even 1000 books a year is considered a huge success. So without the backing of a publisher with a huge marketing budget, you will never ever reach this value.
Let's assume you wrote a bestseller anyway. The problem is that the term 'Bestseller' is not even defined, it's more of a marketing term. Some people say a Bestseller is once you sold 100.000 copies, so let's take that. You write a book which sells for 14 euros and you get 1 euro from this per sale. After taxes, that's about 50.000 euro you get from your bestseller, in total. You can live on that for one or two years, but that's it. You will not become rich, unless you write a top bestseller like Harry Potter. But that's a bit unrealistic.
It's sad that it's like that, I think a lot more people would write and create interesting books if they could make a living from it. The problem is still that the publishers are taking most of your money without actually doing a lot for this, just like in the music industry. But with eBooks rising, it might get a bit better soon.
Shameless plug: you can get my book in the shops below: It's written in german, and a nice science fiction novel in an end time scenario:

I don't earn much if you buy it, but it feels good if at least some people read it :)