One of the great things about writing a business book is having the time and space to explore an issue properly. You have something you want to say, or an experience you want to share, and a book allows you to do this in a way that feels 'complete'. It allows you to present a well-rounded argument.
If you're being honest with your readers, your case will be built on a solid foundation of evidence. You won't present an ideological view that you then back up with evidence that supports your case, no matter how tenuous, while conveniently ignoring anything to the contrary. That is the domain of neoliberals, climate change deniers and anti-vaxxers.
Rather, you will use real evidence. But what is 'real' evidence?
In the context of a business book, as opposed to an academic dissertation, there are two main forms of evidence.