I have another opionion about this.
I don't think people don't succeed, because they are on other marketers' lists, or because they don't have a proven system. There so many proven systems out there. But people are scared.
They are not sure they can make it.
Their motivation is in the money and that doesn't work.
You have to be passionate about what you're doing, whether it makes you money or not. Then it can work. That's your motivation.
Yeah, fear definitely plays a big part too! And having passion of course. If you're not passionate about what you're doing, most likely you're not going to see success. The reasons above are just other reasons why people don't achieve success. It's a collection of things mixed together, sadly.