I reckon it could be done on a high salary without debt, but it would take enormous discipline and a frugal lifestyle for many years to achieve.
If you have a medium income or a low income, forget it....life's normal expenses would prevent it.
I remember as a young fella, thinking that with a fully paid off roof over my head, then $ 100 a day would suffice. 36.5K pa after tax.
I was into shares back then, and figured that with a rough 5% yield, a $ 1,000 would yield $ 50 per year, or about $ 1 per week.
My goal was then easily broken down to getting $ 700 per week, and I knew I would need to have 700K in my pocket to get there. It seemed very achievable at the time.
Of course, that was before complications like wives, kids, school fees, upgraded houses, medical bills for women and children and everything else life throws at you.
The goal was completely blown out of the water, and new targets were set which made the task an order of magnitude more difficult.
To overcome that wall....debt is essential.