First time home buyer for duplex

[Rocco Grossi]

OK so I have been doing a lot of research utilizing BP, real estate agents, and mortgage lenders. With a mortgage being $1,000 or more, how does anyone generate cash flow with that? I've done numbers on a few properties and according to the 50% rule, I would not be generating any cash flow really. Obviously for my first property I would occupy one unit and rent the other unit out of a duplex. Hypothetical scenario:

Mortgage-$1,100

Duplex at $850 per unit = $1,700 for income

According to 50% rule this property would not generate much cash flow. So my question is, how and why is my mortgage so high? Is there anyway to get a lower mortgage? should I shoot for higher income rental markets? I know the 50% rule is just a rule of thumb but I am still having trouble making sense of the numbers.